The way to buy bitcoin that is most inline with the philosophy of cryptocurrencies is of course to avoid third parties. At LocalBitcoins.com you can by directly from peers located near you.
If you want real bitcoins and some derivatice, Coinbase is the world's largest Bitcoin company and provides both a wallet and simple ways of buying and selling bitcoin. Also, you get 10 dollars for free if you use this link!
If you are interested in any of the many altcoins out there Binance is the place for you. Here you find hundreds of cryptocurrencies to buy or sell. Deposits are not accepted in traditional currencies so you first need to get some bitcoin.