They do work или they does work ? в каком случае употребляем do/does, have/has или was/were? от чего конкретно зависит, пишем мы do или же does, например ?

Смотри, какая схема.

Do - все местоимения, кроме He/She/It
Does - He/She/It
На have то же самое.
Was - единственное число.
Were - множественное число.

К примеру, He has got a dog. He was playing football. They were playing computer games.