You can use a centralized exchange like Coinbase, and that would be convenient. The downside is that there’s no privacy; you have to thoroughly identify yourself and they tell the IRS what you bought. Decentralized exchanges like Bisq or AgoraDesk are more private but you have to buy from someone who’s selling, and on Bisq escrow requirements mean you need Bitcoin to buy Bitcoin.

This site has a list of exchanges without Know Your Customer requirements: