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]
(..) PERCY: Adios, chief. Drop us a card from hell. Let us know if it's hot enough. He's paid what he owed. He's square with the house again... ...so keep your goddamn hands off him. What's up his ass? You. Always. You, Percy. (..)1999 The Green Mile