Forming a party will allow you to share the exp gained while adventuring, and it will also prevent casters with the Perfect Caster feat to avoid hitting their party mates. There is a small exp bonus for travelling with a party.

party [form] [TITLE]
This will form an adventuring party. The person who forms the party is automatically the leader, and only that player may add or remove players, or designate another player as the leader.

party [add|remove|leader] [NAME]
This command allows the leader to add or remove party members, or designate a new leader.

party [join] [TITLE]
This allows you to join a party that you've been invited to. Please note that you need to type in the title exactly as specified by the leader.

party list
This will show every member of your party.

party leave
This allows you to leave your party. If you are the party leader, leadership will be passed on to the first person to join the party.