Tahajjud and witr prayer

I want to pray tahajjud but i dont understand how? I searched on google and some said an amount of pairs rakat u want and then pray witr but another said for example 8 rakats tahajjud and then 3 witr? How do u actually pray tahajjud?

And in witr, if its for example 3 witr, do u have to do 3 surahs or part of it? or is it just the first 2 like normal prayer?