people or persons

We generally use the term 'persons,' and not 'people,' to refer to them as individuals. 'People' lumps them all together as the same and indistinguishable from the other. Its usage is a little tricky.

People are crazy.

Certain persons in this room are heading for trouble.

I'll see if I can't find a better explanation for usage

Persons is very unusual except in formal written notices or legal English, in set phrases such as Missing Persons, or used humorously as in Mesmark's example - the humour comes from the unexpected impersonal style in a situation where the speaker quite clearly knows who s/he's talking about. In normal everyday English we would almost always use people in both speech and writing, so the best rule for most lower level students is 1 person (sing) 2 people (pl).
Hope that helps!