As Stefano said it depends on the content. Most people would refer to people in general. Most of the people would refer to a particular group of people. For example: Most people have access to the Internet. Most of the people who live on my street have access to the Internet.

Depends on the context. Either can be correct. Correct: Most people like pizza. Incorrect/Awkward: Most of the people like pizza (as general statement about all people) Correct: Most of the people [here/in America/at the restaurant] like pizza (as a statement about a specific group of people) Correct: Most people here like pizza.

It really depends on the context. Could you please tell us what context would you insert these expressions in?

"Most people" is correct.