Hi Elka!
I'm sorry that I haven't gotten your e-mail yet. My mail server is flakey today; I haven't gotten any mail at all, although I'm sure that there are several hundred pieces of spam and a handful of actual letters in there, if I could only connect to it.

Okay, about BodyPaint...
There are tons of tutorials out there, as you'll see if you Goggle BodyPaint. But most (in my experience) don't tell you what you need to know to get up and running in SL. So here goes.
First; the .obj models as provided by the Lindens are great for Poser, but not optimized for BodyPaint. It takes a little work to get them ready, so I've done that. You can download them, as C4D files with empty textures associated with them,
here. (Clicking that link will start the download, so be aware of that when you click.)
Unzip that file, and put the folder inside it someplace, anyplace, on your hard drive.
Open BodyPaint.
The first thing you need to do is change the Layout, so that you're looking at the same thing I'm going to be talking about.
So, in the Window menu at the top, go to Layout > Load Layout. Browse to the "SLAvatars-BodyPaint" folder you downloaded, to the "Layout" folder inside it, and choose "RW Paint.l4d"
BodyPaint will disappear. Don't be alarmed; it's just changing the layout, and will be back in a nano-jiffy looking a little different.
Now go to File > Open, to the "SL-Female" folder, and click on "SL_Female_Ready.c4d". The familiar mannequin will open in the window, with a white material all over her. At the same time, the grid lines and things will vanish. That's okay, you don't really need them.
To prepare to paint, click on the Brush icon in the toolbar on the left, (about half-way down, on the left side,) and make sure that the 3D Painting Mode icon is also highlighted. (It looks like a Brush and a painter's palette, fourth from the top on the left.)
To pick a color, use the Color palette on the right. (It's probably set to White, so anything you paint will be invisible if you don't change it.) Choose your Hue from the rainbow bar, and the Saturation and Value from the rectangle below that. Or use the sliders if you prefer. The color chosen will show in the Color Swatch on the left of the palette.
You can "save" colors, to make them easy to reuse, by dragging from the Color Swatch to the row of rectangles directly below it. White, Black, Red, Green, and Blue are already there, and the others all look black. Just drag from the swatch to any of those black rectangles, and your color will be there.
The thing below the Saved Colors is a mixing palette. Drag the color from the swatch into any of the narrow rectangles on the sides of it, and you'll see the colors blending in the middle. Click anywhere in that mixing palette, and the color you click on will appear in the Color Swatch (and also become the active color for the brush.)
To paint in Projection Paint mode (which is the best thing in BodyPaint,) click the Projection Paint icon in the Toolbar on the left (fourth from the top - it looks like a checkered globe with a paintbrush and a square, just to the right of the Brush-and-Palette 3D Painting Mode icon.)
Now when you paint, instead of having the brush circle follow the contours of the model, changing size abruptly when passing over seams and things, it will paint straight on the model from your viewpoint, allowing you to paint smoothly across the various maps.
Be careful with this, though; the stroke can get elongated on the sides of the model. I recommend only painting in the center of whatever angle you are viewing the model from, moving the model around to paint other angles.
To enlarge the Brush tip click the right bracket key (]). This works exactly the same way it does in PS, which is very handy. (And a great relief, I must say.

)
To shrink the Brush tip click the left bracket key ([). Once again, just like PS.
To discard the Projection Paint in case you decide you don't like
anything you just painted, click the the icon directly below the Projection Paint icon. (Looks like the Projection Paint with a red X.)
To discard just some of the Projection Paint click the Eraser icon, just below the Paint icon. (Flipping the pen on the Wacom tablet won't work, sadly. You have to use the Icon. And the tip size will be whatever the Paintbrush tip is. Unlike PS, you can't have different tips for different tools.) Then erase the part you don't want.
To apply the Projection Paint click the Apply icon, with the Green Check directly below the Projection Paint, or just move the model. Once the Projection Paint has been applied, the eraser won't work on that part of the layer unless you leave Projection Paint mode by clicking the Projection Paint icon again to disable it, by the way. (That one caught me.)
To move the model hold the 1 key and drag to Pan. Hold the 2 key and drag left to Zoom out, or right to Zoom in. Hold the 3 key, or Option/alt, to do the "virtual trackball" thing, and swivel the model around. To restore the model to the default size in the middle of the window, tap H. You can also choose a different camera from the Camera menu under the View tab; if you do, the model will become tiny. Tap the H key to restore it to usable size.
To change to a different kind of brush click the Active Tool tab on the top right (above the Color palette.) The Color Palette will be hidden, and you'll be able to see the Brush Palette instead. There's more there than I can go into right now, but since you're used to PS, you should be able to work with it. Ask specific questions, if you have 'em.
To look at the 2D painting you are making click on the Texture tab, at the top of the viewport. Then choose the material you want to see from the Textures menu under that tab. (Head_Color, Lowerbody_Color, etc.)
To see the UV mesh projected on the texture, go to UV Mesh > Texture Tags and choose the only menu item there. (What it says will depend on which model you're looking at.) You'll need to do this for each material, but once you have, it will show properly after that.
To paint on only one Material click the blue pencil next to the material name, in the Materials palette on the bottom right. If the pencil icon is dim, the material won't be painted on. Shift-Click to paint on several at once.
To see the Material Layers, click the + sign to the left of the Material Name if the word Color doesn't appear below it, to show it. If it's showing, click the black flippy triangle to the left to show the layers. Right click on a Layer to get the menu that allows you to add new ones, save the texture, and all that stuff.
To name a Layer click on the Layer, to highlight it, then click on the Attributes tab at the top right (with the Color and Active Tool tabs.) Change the name in the Basic Properties field. You can change other stuff there, too; it'll be familiar from PS.
You can also save the material you're working on, open it in PS, work on it there, and reload it into BP.
To Reload an image after working on it in PS click on the sphere preview for that material, to open the Material dialog. In the middle of that dialog, you'll see the name of the image. (You can change it, if you want, by the way.) Click on the flippy to the right of that, and choose "Reload Image" from the menu.
WARNING! Special layers (Smart Objects, Adjustment layers, Pattern layers, etc.) are not supported in BodyPaint. If you open a PS file that has such layers in BP, they will not display properly, and will be lost forever if you save the file. So work on copies of such files ONLY.
To load a new material texture click on the sphere preview for that material to open the Material dialog, and click on the Image button in about the middle. Browse to the Material you want, and open it. It will replace the material currently there, and show instantly on the model. (DO pay attention to the warning above before you load a layered PS material, though.)
This is the way to Preview the stuff you've already made, by the way. Then just add a layer and paint any corrections etc. on it, save it, and open that file in PS to incorporate those corrections into your layered file. (That's how I do it, anyway.)
There is a
lot more to BodyPaint than this, and most of what it does isn't useful for SL (things like painting the Bumpmap, Specularity, and Color all at once, for instance.) But this covers most of the things that had me waving my arms about when I was trying to figure it out, anyway.

Hope this helps!