When to use were vs wa?

Answer 1

When the statement being made is about a situation in the past that actually occurred (not a hypothetical situation), then was is for singular subjects, and were is for plural.

"I was there."

"They were not there."

"We were there."

"You and I were there."

Exception: even though the subject you is singular, you use were.

"You were there."

For situations where what you are saying is contrary to the facts (a hypothetical situation), were is always used.

You are not feeling good, so you say, "If I were feeling well I would go."

The organisms in questions are not in fact birds, so you say, "If they were birds they would have wings."