The word "can" is usually used as a modal verb to describe a person’s ability or what a person is allowed to do:
She can speak English well. (Notice the vowel sound is a schwa, similar to a short e.)
They can drive a car.
I can play golf tomorrow.
You can borrow my car. (You may borrow my car. The words "can" and "may" are similar. See the note below.)
The children can’t go outside today. It’s too cold.
To learn more about "can" as a modal verb, click here.
It’s also possible to use the word "can" as a main verb:
Rita got canned. (She was fired.)
The employees were canned for goofing around on the job. (They lost their jobs.)
We’re canning tomatoes this weekend. (can = to put vegetables or fruit in jars to preserve them for future use.
If I get a good tomato crop, I can them for the winter.
As a noun, the word "can" has many different uses:
Throw that garbage in the can. (can = trash can)
Tony went to the can. (can = bathroom)
Laura is lazy. She sits around on her can all day while watching TV or talking on the phone. (can = rear end; but)
The company has a few films in the can, but they won’t be released until next year. (in the can = a product is finished, usually a film project but it can be other than that.)
Note: When granting permission or when saying it’s okay to do something, the word "may" is preferred over the word "can" by some English teachers and purists. I, personally, don’t care whether or not a person uses "may" or "can" in this instance.
You may borrow my car.
You can borrow my car.
Same thing. In fact, I always use "can" in a situation like this. The word "may" sounds too formal. But that’s just me.