Anything that does not explicitly specify a drive is relative to the working directory, so the period has no real meaning on Windows. The working directory is often the same as the executable directory but could be different if the executable changes it at run-time, it is run under Visual Studio, or run from a .bat file located elsewhere (the working directory will be that of the .bat file).
If you run it from the command line as in your example, the working directory would be “C:/path/to/folder/”.
Absolute paths begin with / and everything else is relative, though there are special cases such as “~/”.
I don’t know.