Coinbase, and Making Transactions

Hello, I have a few questions revolving around an app called Coinbase and being able to make purchases with Litecoin, also a question about how to transfer Litecoins back to dollars. With my research I found an app called Coinbase that allows me to purchase several different crypto currencies including Litecoin. Is this the correct app to use?
I’m not sure whether I can make purchases with this app or not. Once I buy Litecoins how will I be able to convert them back to dollars as time goes on?