On markets.com you can trade so called CFD:s, a derivative that lets you speculate in price changes of Bitcoin, as well as other cryptocurrencies such as Litecoin, Ether, Dash etc. For the daredevils out there.
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.