If someone asks you to send your money for the airdrop, this is fraud. The very meaning of airdrop is the free distribution of tokens. To receive them you may need to either fill out the form or register in the whitelist.
But do not send any money to anyone, do not give your passwords and specify not your main e-mail, as many projects are fraud. You will receive a lot of useless spam messages. Like "You won something - send us money and get a prize", "only you are offered a closed sale, send money and get a 100% bonus."
Do not believe this ever.
Thanks. The one I joined though does not involve any substantial amount, just send 0 ether, so I guess just few cents to spare for the network cost and once you send it you will then receive the airdrop coins instantly. Mostly it will be around 3K coins something like that. Perhaps it's just some ambitious dudes who wants to initiate a project, they will generate coins using ethereum network create a contract and make an announcement to participate and once they see many participants that's the only time they will start in doing the project. Due to lack of knowledge and planning I bet mostly will fail but I am hoping to see someone finding a bit of success like being able to lunch a product, or create a whitepaper.