1 człowiek
2,3,4,5,6.... ludzi
1 osoba
2,3,4,5,6.... osoby
this is the diffrent. Ludzie is plural of człowiek. You can use them how you want, both means almost the same, but ludzie is more like humans - but for example, you're playing football and you need two people to your team and you can use both:
Potrzeba nam 2 osoby do drużyny.
Potrzeba nam 2 ludzi do drużyny.
(We need 2 people to team)