I've already tried joining one or two of these and honestly it's pretty straightforward in theory: you go in, follow the creator or brand's account, do the challenge (usually dancing, lip-sync, that kind of thing), use the specific hashtag, and you're done. Then you're entered into a raffle or contest where the winners get picked. You don't need to be a mega influencer to try, the truth is pretty much anyone with an active account can sign up in most cases.
The thing I see people missing is that not every contest that pops up is legit, but the official ones come straight from verified platform accounts or actual well-known brands. When it's the real deal, TikTok makes it clear in the participation terms and in the video description. About the money actually hitting your account: if it's a legit contest, people say it takes a few weeks because it needs to process, but it does come through. The problem is the scams, which ask for personal info or want you to invest something before you get the prize - that's a guaranteed bust.
My advice: be suspicious of any contest asking you to click external links, share your banking details right off the bat, or anything that seems sketchy. Real contests run right inside the platform, with transparent raffles and direct communication through DM. If the creator has a history of other paid giveaways and the account's verified, then it's worth a shot.