Classic mythic dungeon, how to begin?

Can someone link me a guide how to Start doing mythic dungeons? Most replies here are "you can't queue up, you need to find a group", all groups I tried to join declined me. Probably I am missing something but it is never explained ingame, for example what are the numbers in the groups finder - +10 +20 +25 etc? What is the number after the name of the dungeon in the group description - the item level?Google searches begin with "in order to start mythic dungeon you take the key from your previous mythic run". To be honest I am astonished such an important part of the game is so poorly introduced, I've been playing WoW for a while and I am used to googling stuff and watching lore videos to catch up, but a newer player would never reach this kind of contentPlease help. via /r/wow https://ift.tt/ATjmU0F