"forking" is what happens when someone takes some existing source code, creates their own copy, and adds their own modifications. The new copy is traditionally called a "branch", the divergence point is called a fork, and the act of creating a new branch is "to fork the code." Those are pretty standard industry terms.
Is this the place to ask some questions to clarify things that will seem pretty humdrum to you advanced developers?
The Arduino forums in general, yes.
The "bootloader issues" sub-topic, probably not. Check out the other topics, and pick the one that is most appropriate. "Microcontrollers" for questions specific to the tiny85, "Project Guidance" for general project questions, etc.
This thread probably should have been in "Installation and troubleshooting", but "bootloader issues" was close enough that no-one felt the need to move it.