a guy

A "guy" is a man. It's a casual word.

You use this word instead of "man" when you're talking to your friends or in a casual situation like at a party. The person you're talking about can either be someone that you know, or someone who you don't know but don't have high respect for.

For a stranger who seems older and more respectable, "man" or even "gentleman" are more polite.

Note that you can use the plural form, "guys", when you're talking to a group of men or women:

Great job today, guys. Keep up the good work.

But "guy" (singular) always refers to a man.

happen to (do something)

Use the phrase "happen to ___" to talk about something that doesn't seem very likely. One way this is useful is for asking questions, even though you don't think the listener will know the answer:

Do you happen to know a guy by the name of Fred Breedlove?

In this example, you ask "Do you happen to..." because you think that the listener probably doesn't know this person. You would ask this question if this person was from the same town as Fred, or went to the same large university as Fred, or worked at the same large company.

You can also use "happen to ___" to ask questions politely, even when you do think the listener's answer will be "yes":

Excuse me, would you happen to have a pen I could borrow?

"Have", "see", and "know" are the most common verbs that follow "happen to".

(someone) by the name of (a name)

Talk about a person this way when you think that your listener probably doesn't know who the person is:

There's a man by the name of Tom Johnson who owns a hardware store in that neighborhood. Have you ever met him?

It was founded in the late '30s by a woman by the name of Eloise LaPointe.

This is casual spoken English. Don't use it in writing.