"A ton" is literally a weight that's equal to 2,000 pounds (910 kilograms).

In normal conversation, when you talk about "tons of" something, it's usually an exaggeration that really means "a lot of".

Don't worry, we've got tons of time before takeoff.

I ate tons of food.

This is a casual way of speaking, and is usually used by younger people. It can be used in blog posts and when chatting with friends, but not in formal writing for school.