I got hooked and made some (a nice amount) of money when I put a few hundred dollars in Robinhood, the no-fees model makes buying and selling cheap and easy, so it was fun to use and cheap too.

Is there anything similar where I can do the same with my BTC?    I am fine with minimal fees, but is there a place or way where I can buy/sell from BTC to USD or something similar, where it doesn't become expensive if I use it a lot?   Are there any Robinhood-type exchanges or places to trade in the world of Crypto and take advantage of the market fluctuating?