There are certain characters that never appear in folder names, some of those characters are delimiting characters such as forward-slash and backslash. The path "/folder1/folder2/" means that there is a folder named "folder1" and inside it is "folder2". A folder path can use either type of slash to delimit folders, but generally only one type within a path for consistency.
A colon is used near the beginning of a file path to indicate various special starting locations. Single letters like "C:" are used to indicate drive names. Godot uses "user:" and "res:" as shorthand for the user's appdata folder and the program folder respectively.
The instructions for this mod are provided for Windows and each OS organizes it's folders differently, so if you are using a different OS then you will need to use different paths and acquire the appropriate executable.
That all said, you shouldn't need to make the mod folder. The mod is simply designed to be extracted, moved into place, and played. If you still have trouble installing, I recommend the Strive Discord(https://itch.io/t/284398/discord) as a place to get fast help.