How to join domain

You can't join a domain (assuming you mean a windows active directory domain) without an administrator of that domain allowing you to join the domain. Check with the domain administrator.

Some domain administrators allow a limited number of machines to join the domain if the user has a valid account in the domain. Most do not for security reasons. Start with your domain admin for help on this one.

Just a tip here. When asking a question its best to give us a full description of the problem. Like what domain are you trying to join, what problems are you having, what OS on your computer and the server and anything else that might be relevant. The more you put into a question the better we can answer.