How do you play diablo 2 online with people?

Register with Battlenet and choose the server that suits your area. If you want good connections and most joinable games, go on closed(you cant hack on here or use your single player charectors). If you want to use your hacked charectors and single player charectors, you will have to use open battelnet whitch has a very slight chance you will find a joinable game unless its dueling.