I would get him into the vet as soon as possible. How they treat it will depend on how bad the crack/break is. Depending on how far out it grows they may want to clip the beak back as far as possible without actually causing more damage and then use a glue like substance to help hold it firm. Other times they use almost like a plaster cast type covering that helps make the beak stronger, allows them to still use it and eat normally. It will depend on the vet and the break.

As far as caring for your bird until the vet appointment. No more nuts or anything that is very hard until the vet tells you how to treat. If she/he will eat softer foods switch to them.