Remember that the 3rd conditional is used to imagine the possible results of an event that did not actually happen.
This is the way we imagine how things could have been different in the past. If something had been different, something else would have happened.
He would have got the job if he had not arrived late for the interview.
You would have passed the test if you had studied for it.
If you had asked me, I would have helped you.
What would you have done if you had missed the bus?
I would have been so angry if he had said that to me.
She would have been sorry if she had missed the deadline.
If you had told me, I would have gone.
If it hadn't started raining, we would have gone for a swim.
Would you have gone if you had known about it?
If I had known that I must dress up for the party, I would have bought a new dress.
Those were ten examples of sentences using the 3rd Conditional, now you create ten more for practice.