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.