did you search the forum first?
i'm guessing not...
this question has been asked lots of times so searching will find you a few discussions on what would suit you best.
i know it's tempting to just wack down a thread quickly before searching or you may have thought your question was entirely new but this forum has not far off 10,000 users and as much as your parents would like you to believe it, you're not unique
that being said i would personally recommend Physx as it's what i use and i found it much easier to understand and get into than when i tried to use Newton.
other people will suggest things like Newton, ODE or Bullet. You could try doing a bit of research on each, take a peek at their tutorials and see which seem the easiest to follow to you.