have, has or had?

We use ‘have’ with ‘you’ and ‘we’.
You have bad breath.
We have a vegetable garden.

And ‘they’ and ‘I’.
They have bad taste. 
I have a new car.

All other times we use ‘have’ with a plural subject.
The dogs have worms.
Sam and Jack have bad breath.

If the subject is singular (except for ‘you’ and ‘I’) we use ‘has’.
The dog has worms.
The university has excellent facilities.
She has long hair.

The past tense form is ‘had’. It's used with both singular and plural subjects.
The dogs had worms last month.
The dog had worms last month.
Both the dog and the cat had worms last month.