Just log in; all mods are server side, so you don't need to do anything, but you may want pvp mods like radar, etc. Since there are no rules, there definitely are some full time robbers on the server who will kill you just for the fun of it. I would recommend you take a little time on the subreddit to read about the mods, because they pretty dramatically affect gameplay. Because the server intends to encourage cooperation, it's difficult, but not impossible to live as a hermit. Things like iron farms and xp grinders have been disabled, as well. And, the vanilla ore distribution has been reduced to one sixth, so you'll have to look harder for iron/diamonds.
What many new players do is browse the subreddits of some of the cities until they find one that appeals to them. If you express your interest to join that city, they will likely set you up with some food/land/gear depending on how they operate.
Ive been thinking... Ive been thinking real hard.:hmm: I might just try to make a multiplayer world on my websites server. Because i am legally a lawyer on my mothers court case i may win the money to run a large multiplayer server(politically themed, no rules except greefing) for about a year. Assuming i can set it up i will allow the orbiter community and then some to join.