I have seen so many threads that do not understand how to cut a basic hole in a wall so I thought I would write a quick tutorial on how it is done.

Firstly create a wall using the block tool.



Then draw a block going through it, make it the size you want the hole. This is just for visual help when cutting the wall.



Now select your larger outer block that you want to cut the hole in and draw a line along the top of the visual aid object using the clip tool (Has a couple of squares going round it on my screenshot)



Now keep clicking on the 'Clipping' tool button until both sides othe shape are white.



Now press 'Enter' or 'Return' and it will cut the object. Then select what section you need to cut next.



Cut that peice in 2, and then select the next section and do the same, and keep going until it looks like this.



Now delete the visual aid box with you wanted to cut out around.



Now delete the section where you want the hole to be.



You may want to group the objects together afterwards by selecting them all 1 by 1 holding down Ctrl and then 'Tools' >> 'Group'