Simple, it adds to the game the Fallout's Stimpak, basically is like a regeneration potion, speed and resistance, all mixed in one item for emergency
First, you need the Empty Stimpak, wich is crafted with:

Then, to craft the Stimpak, you need to use:

Then all you need is to right-click, and all is done!
Also, it remove the bad effects you are carrying on and bring you this

Credits to Bethesda, Fallout Games & Series