i dont have the subtrack button as you do in blender i only have simplify
Subtract is an option I added in a modified version of the script. The link to the modified version is in the description of this lesson's overview page.
It is in the description:
This is the link: https://s3.amazonaws.com/blendercookie/tutorials/2014/blender_modeling_sci-fi-helmet/blender-sculpt-tools-master.zip
the script doesnt work it says draw a line with grease pencil first and i do draw a box
also when i cut it doesnt remove the piece it just splits it in to i have subtrackt on
The script has been finicky since the first time I used it. I often have to repeat an operation, like subtract, multiple times before it does what I want. While the repetition is annoying, I can't recall a time where it didn't do what I wanted eventually.
Unfortunately neither script is actively maintained. If continue to get issues, I recommend downloading the version of Blender this video was recorded with and trying the addon there.