When cashing out your crypto, depending on the payment methods available to you, you can either transfer, "cash out" your funds to your bank, or leave your cash balance for future crypto purchases. Coinbase does not limit selling crypto to your cash balance.
To sell your crypto:
Sign in to your Coinbase account on the web or mobile app.
Select Buy & Sell.
Select Sell.
Select the crypto you want to sell and the amount.
If on mobile, you'll be required to select the asset you want to sell before entering an amount.
Change the To destination, if applicable.
It is likely that this will default to your local currency balance (USD) but you may have the option of adding to another balance (e.g. USDC).
Select Review order.
Select Sell now to complete the sale.
Once the crypto sell is complete, the funds will be available in your cash balance to buy other assets or cash out to your bank.