Reverse DNS maps hostnames and domains to your IP address blocks. If you've been assigned control over your own netblocks by your upstream and you want to have control over your reverse mappings, you can do that here.
Without valid reverse DNS in place for your IP addresses you will find various "trust" levels about your network will be lower, your email servers will have a harder time sending email or may be blocked altogether.
Note: Before reverse DNS can be managed here, your upstream address allocator must delegate your netblock to our nameservers. See the help docs about the various ways to do this.