Person, persons or people?

We use person in the singular to refer to any human being:

• Joel is such a nice person.
• She's a person I have a lot of respect for.

Persons (plural) is a very formal word. We only use it in rather legalistic contexts:

• [notice in a lift]
  Any person or persons found in possession of illegal substances will be prosecuted.

To refer to groups of human beings or humans in general, we use people:

• I saw three people standing on the corner.
• Not: I saw three persons ...
• Jim and Wendy are such nice people.
• People are generally very selfish.
• Three people were interviewed for the job, but only one person had the right qualifications and experience.