Make sure the post is 'square' to the floor. [=make sure that there is a right angle where the post and the floor meet]
I'll go on the trip if I can 'square it with' my parents. [=if my parents will agree to let me go]
Here's the rest of the money. Now we're 'square'. [=now we don't owe each other anything]
(..) Don't... Survival, evasion, resistance and escape. This is it, tadpoles. Your target is inside an area of five square miles. When and if you locate this facility, you gather up as much intel as possible within the allotted time frame... and get (..)1997 G.I. Jane