"Il lit pendant qu'il mange."
Translation:He reads while he eats.
« Pendant que/qu' » as a whole is a conjunction meaning "while." It connects two parts of a sentence together.
can this be used to talk about a single person and used in the same way to talk about two people?
It's possible that this could be about one person or two, context would tell. If the pronouns are the same, it typically is assumed to be the same person, but lacking context, most speakers would use a proper noun instead of "il".