Can you convert Coinbase to USD?

Excuse me, I'm a bit confused about something. I've been hearing a lot about Coinbase and how it's a popular platform for buying and selling cryptocurrencies. But I'm wondering, can you actually convert Coinbase itself into US dollars? Or is it more about converting the cryptocurrencies you hold on Coinbase into USD? I'm trying to understand the process better and how it works. Thanks for your help!