What is the Skellet Generator and how do I find where "Build.txt" is
Hey Mr chicken!
The Skelton gemerator is a tool to create the basic structure of a mod, the stuff you don't really want to tinker with it you don't know what you're doing. You can now use the in-game method of creating this so called Skeleton, hop into the Terraria DLC (free) TModLoader for free or download and install it yourself if you don't have the game on steam.
The files you need are all stored in the skeleton. You can, as said before, create the skeleton in-game, just follow these instructions (only that paragraph).
If it was successful, your source folder where the mod is should open, you can then select that folder in TModMaker and it should work like a charm!
Please let me know if you still need help! Have a nice day!