Layers or Masks? Beginner with photoshop.

[Lola]

Hello Everyone, Can someone tell me how to use Layers or Masks? I have two photos. One is my son and I'm wanting to get rid of the background (people) and the second is what I want as the replacement background(foliage). I'd upload them so you could see but can't figure out how to do that either....ugh. I'm not very good with the PS lingo and have read the book I have, only to confuse myself more. Any help on how to do this would be great. Thanks much.