New players that're computer generated with random stats and potential to counter retirements and to have a realistic youth system, as your game progresses, these willl be more and more important.
They are basically the same as the other player's, so you can scout them and buy them etc etc. But regens have a really silly face, that's how you'll recognize them!
Easiest way... look in your youth team. Every team generates newgens each year. If you're looking to find the best ones then there are plenty of threads on this forum about scouting.