I found an old harmonica, what kind of harmonica it is?

It's a Lee Oskar in the key of A. I have one myself that's identical. The LO and the Hohner Special 20 are the two most common models played by blues and rock artists, probably country too. These are what are called "diatonic" models and are what the YouTube videos are aimed at. They likely use a C, so you'll sound different, but it's a good harp.

Remember, somebody else has been kissing this thing, so I'd clean it good first. I take the things apart (there are some small screws that hold the covers on and the brass reed plates to the plastic comb. I use a toothbrush and diluted mouthwash, rinse the pieces, make sure they're dry, then reassemble. You can't really screw up reassembling them if you don't lose the screws.