How and where should I register my server as an nameserver.

You can register it at your registrar. Which one do you use ? Also make sure your host has created the nameservers for you first.

You should do this with your registrar. Who do you use right now?

I have an own server in my home and I want to play with it.
I have register the domains with namecheap and Rackshack.

Can anyone explain how