Everything you need to know should be covered in the tutorial when you first join a server. Anything, and I mean, anything else you need to know about the servers is in the Empire Guide. You can find this at the top of the website. For easy access though: http://empireminecraft.com/guide/ The commands you are after are: /visit open This will take you to a random free lot each time you type it. Once you find one you like simply type /claim addressnumber e.g if you are on lot 1234 then type /claim 1234. Hope this helps.
