Sorry, dave, but the question has been asked before. If you would of searched you'd of found the answer.
You have to apply at a town to get an invite. But be warned, almost all the towns are full, so you might not get an invite from them. Also there is a section in the forums that deals with town recruitment. It tells what towns are accepting members, which are full and who's building. Check it out, before you go asking for invites.