Hehe..
I was where you are now only a few weeks ago. Lots of friendly people more than happy to provide advice..
Manifest.entity and string.entity are to be found in the mods folder where the gameinfo folder is located.
They are written in plain text.
manifest contains a list of all files for the game while string contains a list of information for everything in the game.
Both files are count numbers that must be updated after adding or deleting anything.
VERY IMPORTANT TO KEEP TRACK..
can`t begin to state how frustrating it is to loose count..
just do a "search" for the info you want to change and you should find every reference..
It might be a good idea to take copies of the original files before you start meddling- in case you end up breaking something..