When I bought my BitCoin, I paid €3 to Coinbase as a flat fee. Later I transferred some to a paper wallet to buy a coffee, this happened :
![](https://uploads.tapatalk-cdn.com/20171205/d55486359ad07c4c3caef90e65274a35.jpg)
To answer your question, Coinbase is an exchange with a website and an app. You have several wallets (dollar, euro, BitCoin, Ethereum, etc). You can move money in and out of the euro and dollar accounts to your bank account or credit card at the touch of a button.
If you want to buy BitCoin, you specify that you would like to take money out of your € account and buy a certain amount of BitCoin. Then the amount of BitCoin appears in your BitCoin account. You can transfer this away and keep it somewhere else if you wish. If you sell BTC, the money goes into your dollar or euro account and you can move it to your bank account or credit card if you like.
I think there's plenty of other ways to do it but this way is expensive and simple.