Step one: go to files.minecraftforge.net
Step two: find out what version of minecraft jurassicraft runs on
Step three: download the recommended INSTALLER for the version of minecraft you found
Step four: run the installer, follow the instructions
Step five: drag and drop whatever jurassicraft download file you got into the mods folder.
to find this folder, open up the task menu thingy, and type %appdata%.
open the .minecraft folder, and locate the mods folder.
Step six: when you open up minecraft, please be sure to select whatever profile the forge installer had you set up.