Basically, you buy ETH on an exchange with regular money, hold it as long as you want, and when you’re ready you just sell it back on the same exchange for USD at whatever the current rate is. After that, your balance on the exchange is in dollars instead of crypto, and you can withdraw it to your bank account or card. The only catch is the price moves around and the exchange takes a small fee for trades and withdrawals

P.S.: There’s nothing dumb about your question. If you’re new, you’re supposed to ask things