Guild Wars 2

Can someone teach me the fight against trio?

i wanna learn to join others groups when they ask for Exp people for it.

I have never done it so cant help teach it, but since you have gotten no other responses you might want to check this out if you have not done so already:

http://dulfy.net/2016/03/22/gw2-bandit-trio-salvation-pass-raid-guide/