Active TF2 Mix Groups

EU - 6v6 Mixes: https://discord.gg/haDkVdp
NA - 6v6 New maps: https://discordapp.com/invite/BjyWHF
NA - 7v7 Prolander: https://discord.gg/VNEPZaU
Central America - Mixes Slash
Asia - AsiaFortress' discord

The easiest mode if you have never played competitive is prolander, followed by highlander.
Both play more or less like a pub and don't require meta knowledge outside of what you probably already know from pubs.