When do you use the word 'had' in English?

had- used in past tense. ( I had, we had, ...)

has- present tense of someone elses possession ( she has, he has,...)

have- used in present tense ( I have, you have, we have, they have,
Well, 'have' and 'has' are present tense Words. 'Have' is to use when you are referring to more than one noun, or yourself. 'Has' is when you are only referring to one noun. So, you would use these when something is currently happening, or going on at the moment. 'Had' is a past tense Word, which you would use when you are talking about something that used to be so, or is not anymore.

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Examples:

Example A All of the museums in this town havea science-fiction display.

The Frontwind Museum has a science- fiction display.

The Baxterville Museum had a science-fiction museum a few years ago, but took it down due to repair issues.

Example B Lynn and Jacoby have two dogs.

I have a dog named Maxwell.

Michael has a brown dog.

Ed had a dog, but he gave her to his cousin.