Hi, i read from the other posts that i can't use any of the samples... which in want to know more about, is it only the textures that have to be custom or even things like trees, bushes, etc. And also the physics... Must that even be custom made?

Physics? What do you mean with physics? (If you mean the code no that has not to be done by yourself)
All the assets however ,animations,models (also vegetation),textures,sounds etc. , need to be mad by yourself if you want to sell your game.

Short answer

If it is a commercial game (meaning you have a indie license and you are going to sell it): Then ALL assets have to be made by you (models, textures, particles, EVERYTHING)

If on the other hand it is a free game (Non-Commercial) then you can use whatever assets from the SDK you want.

... That wasn't so short....

So no assets from Crysis 1 or Crysis 2 are allowed, even if it's a free game, correct?

Y, no Crysis / FarCry assets.