If you're talking about a Roblox Chat Party like thingy, you can't join them. You have to be invited. Best way to do that is to invite them to a chat, easily done... If they allow that. Then ask them if you can join their party. If they're the party leader, they will most likely invite you, or if they are a party member, they will ask the party leader to invite you. BUT. There's a terrible possibility they're doing something else and will be afk. :P <<< Soo terrible. Jk. Well. Yeah. Back to le question, you can't join a party in Roblox. :P
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You cannot join parties in Roblox. The only way to be in a party is to get the party leader to invite you or create one yourself.
The millionth player on roblox is 2COOLFORU.
ROBLOX AND BUILDER MAN
There are many non-official "clans" on Roblox. To join a clan you have to find the clan leader and ask him/her.
John Doe was the first to join and the first to leave then Jane Doe came along THEN roblox