I don't understand. If i want to go on vacation for instance, what happens?

Idle and Classic are two versions of Warzone. Idle is as the title suggests, an idle based map game. Classic is a multiplayer risk clone. Hope this helps

Vacations are a feature for Classic to prevent being kicked from a game, but not all games honour vacations.

See https://www.warzone.com/wiki/Vacations as well for the details.

Like Dan mentioned, unfortunately not all games respect vacations, so the chances of your vacation ending early due to you having to commit are decent...

But thats only relevant if you really want to go completely AFK.
Most people just get the app (https://www.warzone.com/mobile) and play their games on the go if they have a few spare minutes.