How do you make a sentence for was and were?

You say was to describe one thing (singular noun) and were to describe more than one thing (plural noun). That's the general rule.

So:

There was a big storm.

There was a cat sitting on the wall.

We were very cold.

There were 20 people at the party.

There was lots of rubbish. (Rubbish is a singular noun, so this fits the rule.)

The verb of a sentence must agree with the subject in number and in person.

• Instead of: What was Stephen and Laura like as school children?
• Consider: What were Stephen and Laura like as school children?