Basically all you need to do is download the server software from mincecraft.net, now there are to options. You can either have the server authenticate with the minecraft logon server which would require everyone to have a payed for copy of the game. or you may run it without the authentication and anyone with the same version of the game may join. There is a whitelist included which basically if enable only allows people on the server if their names are on the list. Personally i think the whitelist is good because it stops people from smurfing and changing their nicknames every 5min.
