what does ahead of any installs of python or git mean? does it mean something like making a copy of the git files to a new folder at the end of "C:\src\depot_tools\"?
PATH is the environment variable consisting of directories searched for program names. “Ahead of” usually means before; i.e., the directory where depot_tools is should be earlier on PATH (more to the left) than any python or git. (Why? I have no idea... I’m not familiar with the tool.)
Add depot_tools to the start of your PATH (must be ahead of any installs of Python and or git)