To settle a bill or debt. Square refers to the honesty of the deal, and up is the action of payment or performing the task.
To tighten the connections or correct
the angles in a construction project, since squares are made of right angles at exactly
ninety degrees, which is the majority of building connections and materials.
To confirm plans and
reservations, straighten, or organize.
"When I come by tomorrow, I'll square up with you on the loan you gave me."
"If this
drywall's gonna hang right, you better square up that
door frame."
"I got my vacation all
squared up."
"It's supposed to be in the seventies this weekend, so I'm gonna get the lawn squared up."