How do I register a .bit domain name with Namecoin?
The algorithm of registering .bit domain is described, for example, on dot-bit wiki.

In short:


Create new domain name with name_new command: ./namecoind name_new d/&lt;name&gt;
Wait 12 or more blocks
Actually register the domain with name_firstupdate, where &lt;rand&gt; is the second (shorter) hexadecimal string returned by name_new, and &lt;json-value&gt; is the domain configuration (similar to DNS record): 


./namecoind name_firstupdate d/&lt;name&gt; &lt;rand&gt; '&lt;json-value&gt;'

The basic json-string, mapping the domain to the some IP looks like that:

'{"ip":"1.2.3.4", "tor":"123456.onion"}'


More on domain configuration