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?
Yes, cashing out is profit protection but, it is also a stop gain. Follow the exchange user guide for instructions on how to sell or contact their support team, the details of how you do this are exchange specific.
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.