How do I...

I'd like to know how to make holes in objects with the ingame tools, so i can make shelves and stuff?

Hole making is rather limited.

There's a field in the object editor for hole size. Change the value there to a non-zero value and then set the hole shape.

You can't make a hole in a prim unless it's a prim that has a hole option, and then you have to put the hole in the only place that it is allowed (usually centered on the Z-axis). Thus, for example, you can make a hole in a cube or a cylinder or in things derived from them, like cones. Tubes and torii naturally have holes in them.

Beyond those pre-drilled holes, you have only a couple of options:

(1) You can link prims together to surround an open space -- like kids do to make a window or a door in a Lego house. It's a hole, but not a hole in just one prim.

(2) You can "draw" a hole by painting a transparent area in a texture that you apply to a prim. That's how a lot of windows are made in 1-prim walls in SL. It's not a hole at all, but it looks like one.

If you are making sculpties instead of using in-world materials and methods, then you can create holes in them as well.

This sounds very limiting, but it's not. Look around SL and you will see an endless array of great things with holes in them, all made by one of these simple methods.

Since you asked ..... To make a VERY simple bookshelf, just rez a cube prim and use the hole option (in the Edit panel's "Object" tab) to create the biggest hole you can (95%). Flip the prim on its side so the hole is horizontal and --- bingo! -- it's a bookshelf. Make several and stack them and you have a more complicated bookshelf. There are better (or at least more elegant) ways to make good bookshelves, but that's a start. And it looks nicer than the ones you probably made out of cinder blocks and scrap lumber in your first apartment.

Wow, Thanks everyone! I must be blind to have missed that?

Not to waste space on another thread, How do I fuse objects together?

You don't.

You can link objects together, so they move as a group, can be scaled proportionally as a group, and can communicate with each other via link messages, but there aren't operations like weld, trim, intersect, etc. in Second Life building.

And exactly how do i do that?

All I want is a bookshelf/table/chair that stays in one piece!

When you're in build mode, select all the components by dragging a rectangle around them then link them by either ctrl/L or go up to Tools and select Link.
The last component you select will be the root prim and will provide the name for the grouped components.

Hey I must be getting better - I managed to provide an answer to someone else instead of being the question asker!! Yay!

You might want to go to YouTube and search for second life building tutorials. There are a bunch of them.

Also you might try the Ivory Tower of Primitive, a place in Second Life set up to teach building.

There are classes offered by a number of individuals and groups, NCI being the one I can remember the name of. NCI is short for New Citizens Inc., and has one among several places located in the sim called Kuulah.

I believe there is still a building tutorial scripted gizmo at NCI.

Visit definitely The Ivory Tower Library of Prim, Natoma (207, 170, 25)
dont rush through, but take every litle lesson and experiment in a sandbox with everything you are tought. It is an excelent place!
Also, visit the The Particle Laboratory, Teal (180, 73, 21), when you get to the point where you want your builds to ..sparkle

-and, no i do NOT have affiliation to any of the abowe at all