How to include assets: In your Blender scene, go to File > Append, then find the Rock and Gravel Asset Pack.blend file and click it. Next go to the Object directory - inside you will find all the models in the asset pack. Pick the models you want to include in your scenes and press 'Append from Library'. That's it ! The assets are now in your scene and you can move, rotate and scale them to fit your needs.

*** Attention - Be careful of importing all models at once as Blender might hang for a long time, depending on your computers' hardware. ***