Typical restriction
Most states bar new drivers from carrying any non-family teen passengers for the first six months of their intermediate license. Many extend this to twelve months. Family members and adults are usually exempt.
Why the restriction exists
A car full of friends is a car full of distractions. New drivers, who are still building situational awareness, are particularly vulnerable to noise and conversation in the cabin. The crash data is unambiguous: the restriction prevents crashes.
How it is enforced
A police officer who pulls over a new driver for any reason will check the passengers. A passenger violation alone is not usually a stop reason, but it is a routine secondary citation when an officer pulls you over for speed or another minor issue. Penalties typically include extending the time-in-stage and a fine.
Practical advice
For the first year of solo driving, have at most one passenger and ideally no passengers at all. Use the time to build experience without distraction. The restriction lifts itself within a year — there is no need to risk your license for a couple of months of carpooling.