Furdle, you press O in game and then write something in that box that says "server password" and then press save.
I dont want a passworded or whitelisted server.
While the server was work in progress I had it open so people could join, some of which who I banned immediately. When the server was finally finished I lifted all the bans and stopped giving out frequent bans.
When I am building a project I do not want people I don't like coming into my server as they distract me and other builders on my server.
If you have a serious problem about how I run my server here's a tip,
don't join.