Coinbase
This exchange is a great place to start for people completely new to Bitcoin. It is where I began my journey some years ago now and it still offers a great user interface that is easy to navigate. Be aware though, that you don’t really want to store your Bitcoins here long term. The exchange fees are relatively expensive and it is easy to be distracted into buying coins or tokens that are not Bitcoin. If you are completely new to cryptocurrency, become familiar and comfortable with Bitcoin before you try anything else.