There is many platform for playing games with friends/community online among them there is any name come first then that is "Steam".Steam provide large numbers of games to play online/offline, free to play/paid to play/free to download/paid to download.
You can install steam software in your PC and start to find your favorite games start to play it.Steam not provide games only but it provides software related to your pc use also provides by it.
Popular shooting game named Counter Strike Global Offence is popular in steam you can download that game by Steam and join to play competition/tournament which held online by steam and you can also sell/buy CSGO items on Steam.
Steam Provide collection of SinglePlayer/Multyplayer games.It provides good heavy games to small scale games.
Only one problem comes in Steam software that is if your internet is slow/medium then it will take little time to loading.