What does I mean when some on doesn't have a drivers liscense...just an idenfication card.?

It means they can't drive. 

It means that for some reason they do not have a driver's licence (there can be many reasons).

As a driver's licence is commonly used as ID, most adults without one choose to get an I D card 

It means they are not licensed to drive, but have an ID card to prove their age and identity as needed.

Depending where you live it is standard operating procedure a drivers licence allows you the privilege to drive and use for identification. An identification card is almost identical to a driver's lisence but doesn't allow you to drive.

It means they haven't passed the state's driving test and can't drive. In big cities, like New York, most adults don't have driver's licenses. That's because it's very expensive to have a car in the city and with all the mass transportation available, most people never learn to drive, never get a driver's license, never have a need to.