While a single adventurer is a pretty strong guy compared to a normal person, they wouldn't make it very far into a dungeon on their own. This is why adventurers form groups, also called parties, before going into a dungeon.

If you don't have a party, you can start by either asking around in the Adventurer's Tavern to see who wants to go raid a dungeon, or post in the Looking For Party thread to see who is available. Once you get a few people together (most parties are four characters, but there are some tough dungeons out there if you want to have more players, and there are also easier dungeons for smaller groups), you need to nominate a party leader. This party leader will then post in the Dungeon Request thread, listing the party members.

Once the admin makes your dungeon thread, the party leader needs to go there and again post that he is the party leader, who their second-in-command is (who will make decisions if the party leader is unavailable), and everybody in the party needs to post what equips they are bringing in, and that they agree to listen to the party leader and his second-in-command (if they don't agree, they shouldn't be in the party in the first place).

Once the dungeon thread is up, things usually work on a per day basis. Players have a day to post that they are in the party and what they are bringing in, and they have a day to decide where they want to go next in the dungeon or who gets items they found (though the party leader makes the final decision) before the game moves on. In combat, everybody has a day to roll their dice and state their actions for a particular round before the admin in charge of the dungeon assumes that the character does nothing for that round and the combat moves on. If you couldn't post that day that's fine, but the admin can't hold up the game for everybody else.

When the dungeon gets cleared, everybody needs to make final decision on who gets what loot from the dungeon, and everybody needs to post how they spend their character point they got for being in a party that successfully cleared a dungeon. Once all this is decided, the admin will close the thread, update everybody's profile in the Active Adventurers Roster thread, and everybody can decide whether they want to stay in the party or join a new group of adventurers for their next dungeon.