How do I make a door way or window in my home?

[Rolig Loon 26,643]

If you want to make a hole in one prim, the only way to do it is to turn the prim so you are looking down its Z axis and then increase its Hole size from 0 to whatever size you want.  Voila, hole.  (That's on the Object tab of your Build/Edit tool -- CTRL + 3)  The only thing about that method is that a hole is always centered on your prim, and its dimensions are proportional the the length of the X and Y axes.  If you want a perfectly square hole, off center in a rectangular prim, you're out of luck. It's a useful method, therefore, but a limited one. 

Most builders use the Lego method for making doorways and window instead.   Stack a bunch of prims, leaving an opening of exactly the size and shape you want.  That uses more prims, but it is much more versatile and aesthetically pleasing.

The least satisfying method, used only in rather cheap construction but sometimes appropriate for incidental buildings, is not to make a hole at all.  Using Photoshop or your favorite graphics program, create a texture for your wall and draw a window.  Create an alpha mask and, from it, set the window area as nearly pure white in your alpha mask.  When you apply the texture to a prim in SL, the window area is transparent and it's exactly where you want it.  (It's also a 2-D window and creates potential alpha sorting problems elsewhere on the wall .... ).

[Rolig Loon 26,643]

If you want to make a hole in one prim, the only way to do it is to turn the prim so you are looking down its Z axis and then increase its Hole size from 0 to whatever size you want.  Voila, hole.  (That's on the Object tab of your Build/Edit tool -- CTRL + 3)  The only thing about that method is that a hole is always centered on your prim, and its dimensions are proportional the the length of the X and Y axes.  If you want a perfectly square hole, off center in a rectangular prim, you're out of luck. It's a useful method, therefore, but a limited one. 

Most builders use the Lego method for making doorways and window instead.   Stack a bunch of prims, leaving an opening of exactly the size and shape you want.  That uses more prims, but it is much more versatile and aesthetically pleasing.

The least satisfying method, used only in rather cheap construction but sometimes appropriate for incidental buildings, is not to make a hole at all.  Using Photoshop or your favorite graphics program, create a texture for your wall and draw a window.  Create an alpha mask and, from it, set the window area as nearly pure white in your alpha mask.  When you apply the texture to a prim in SL, the window area is transparent and it's exactly where you want it.  (It's also a 2-D window and creates potential alpha sorting problems elsewhere on the wall .... ).

[Lindal Kidd 17,893]

There are several ways to build walls with holes in them, but only one in-world.

1.  Rez a prim.

2.  Use the Hollow box to make a hole in the center.  You can change the shape of the hole with a drop down box near that control.

3.  Rotate the prim 90 degrees so the hole is in the "side" rather than the "top".

Note that you cant' change the position or the proportions of the hole.  This may limit you in ways you don't like.

You can use the Sculpt Generator tool to build a wall out of ordinary prims (including holes for windows), and then turn the prim wall into a one-prim sculpty wall.  This introduces a couple of limitations in terms of texturing the wall and the bounding box.  You won't want to use this method to create a door, because the sculpty's bounding box will prevent you from passing through...unless you turn the entire wall phantom.

You can build a Mesh wall in an external program like Blender.

For a first home, I recommend simply making the wall from more than one prim.  Think of it as a challenge...how few prims can you use to make the wall with the openings you want?