how do i use should with a past tense or what?

Question

example: I should have gone to school

Answer 1

The use of should with the past, similar to your example, would be a 'main' clause in a Third Conditional(or sometimes in a mixed conditional, Second + Third). Conditionals are usually formed of two parts the 'if' clause and the 'main' clause.

Third Conditionals describe:

1. Hypothetical situations in the past, (something that didn't happen, but could have)
or
2. Giving criticism.

Example 1 (Hypothetical Sit.)
If I had wanted to pass the exam, I should have gone to school.

Example 2 (Criticism)
A. "I failed my exam!"
B. "Then you should have gone to school!"

Answer 2

You're right--use should have with the participle for the past tense. If you used the present, you would say, should go to school.

Answer 3

just like you did or should've that may be what you were looking for