When you start the server, at the map select part, you click advanced. then look for game mode. it should have a pull down menu next to it. select capture the dragonball mode.
When in game you gather the dragonballs by simply running up and touching them. They will show up as orange dots on your scouter. When you gather them at one point and they start glowing, you summon the dragon using the B key if you left it at the default. If you changed the default then use that key.