Prim texturing questions

A couple of admittedly newbie questions regarding adding or affecting textures on a prim:

Let's say I have a single prim - a cube. How to I select just one face of that prim to apply a texture to it? I managed it accidentally, once, and haven't been able to do it again since then.

On a flat prim, how do I make it so that from one side it is opaque, but from the other side it is translucent? The Shojii-screen walls on my home are opaque white from the outside. But when inside the home, you can see through them like they were 50% or so transparent. A neat effect! I'd like to duplicate it when I add a similar panel as a door over an open doorway.

Ummmm. OK. Reading another thread I think I may have answered my own first question.

Apparently, dragging a texture to one surface of a prim apples that texture to just that face of the prim. That will be handy for making some very low prim count furnishings, where I can apply a texture of the front of a chest of drawers to one face of a rectangular block, rather than modeling the drawer fronts as very thin prims and placing them on that surface.

If there's any other way to do that, I'd still like to know how.

In edit mode one of the edit options says "Select Texture" check/click that box/circle and then click on the surface you want to texture. You can make all the changes to that one texture, repeats, offsets, rotations etc by selecting the texture that way.

But when you are in 'Select Texture' mode many items in the Tools menu will become unavailable. Don't panic. Just switch back to the 'Select Position' mode when you are done editing textures and the Tools menu will go back to normal.