To repair cracks in the wall, you can do the following:
Buy cement.
Buy Wall Fixer (WIP).
Fill a bucket with water.
Hold the bag of cement and click left on the bucket of water, use the wall fixer in the concrete and click repeatedly on the crack with the wall fixer until it is repaired. Be careful because if you leave the concrete unused for too long, it will harden, making it impossible to use the bucket again.