The PATH environment variable is a PC setting which defines where the operating system might look for executable files. Windows does provide a way to view and edit your PATH, but it's not exactly straightforward: you'll need to right-click Computer, select Properties > Advanced System Settings > Environment Variables, find and double-click "Path", then scroll through a tiny (and non-resizable) window, trying to figure out what it actually contains.
Path Manager, fortunately, is a little easier.
The program doesn't display the usual lengthy string of folders, for instance - it breaks them down into separate lines for easier reading.
If a folder doesn't exist any more then it'll be marked as invalid, helping you to spot problems right away. Or if you're just curious why a particular folder is included at all, then a quick double-click will open it in Explorer, ready for you to check.
Folders can be added to, or removed from the path with a click or two (and if you're not sure of a path then you can browse to it, rather than having to enter the whole thing manually).
And once you've finished, your new variable can be saved, and there are even options to back up all your environment variables or restore them later.