You'll basically lose your money if you do what you refer as an example. You're selling on a loss since you sell when bitcoin goes down. I think the short you are pertaining is on futures trading where you borrow some money and short some cryptocurrency that has a potential to go down and that's the time where you can earn some profit. Spot trading and futures trading is different. Also be careful on trusting these kind of groups since some of them are just trying to manipulate their members into buying and selling so that they can earn in their own gain. They particularly try to pump and dump small altcoins but if it's bitcoin that has a large market capitalization, maybe they are legit in providing help to newbies. Try to back check their past predictions.