how do you make everything disappear after a player leaves?? like if player 1 leaves but he still has 2 cannons its still there when he left and i want to know how you make those cannons leave when the players leave...

When a player leaves their units are given to Player 12, or Neutral, in SCM Draft. So all you have to do is set up your triggers to do what you want when player 12 owns any units, you could remove all units for player 12, or give them to other players, depending on the map.

Note that resources are usually given to player 12 by default, so they may cause issues.

make sure you don't use xtra for it or else if you make the trigger and open it with xtra it will be deleted i think or messed up

I can hardly understand what you just typed. If you mean that Neutral force triggers made in SCMDraft mess up when opened with Xtra Editor/Staredit, you're wrong (at least, I never experienced problems).

you cannot create that trigger with xtra editor because you cannot select player12/neutral. in xtra editor you see a "_" where the player12/neutral would be in more powerful editors. You cannot mess up the triggers unless you select it, change it and save it.