After I have bought a crypto currency at an exchange like Binance can I sell for dollars if it is going down. Basically if I have a profit from a currency what can I do with it to protect it?
If you don't have your private key, and the custodial wallet that does have your private key is no longer accessible, then you cannot move your coins or "cash out".
Invest in a hardware wallet, and transfer your coins out of any custodial wallet if you plan on hodling the coins. That way, if you ever need to cash out, you can.
Yeah, Willtech is right. You can withdraw your assets if exchange you're using allows doing that. By the way, not only Binance offer such an option. It's also possible to cash out with Cex. Just take a look.