should have: You should use should have in a sentence as past tense like "You should have done your chores." I agree with that as: This is used when you are talking about an event that took place...
Should your decision be accepted, I will miss you. Which way should we go? Should this go here or there? Why should I do the work? You should, but don't. Should there be something else to go with...
was and were are the simple past of the verb 'to be' so: I am (ill) = I was (ill) You are (pretty) = You were (pretty) He/She/It is (at home) = He/She/It was (at home) We are (single) = We were...