Just like internet favourites, web pages can have multiple files in folders and multiple folders in folders.
When drawn out this looks like a family tree with parent pages (folders) and child pages (folder or files, folders have files branching from them but files wont have folders branching from them, a file becomes a folder when it has another file branching from it)
When linking further into a website (to navigate the website) it is important to follow the hierarchy down (from the index page) and back up (to the the index page). There are seperate ways to go up and down.
If going from the index page through a few folders to a file you would put in the following: folder#1/folder#2/file
eg: to get from the ‘index’ folder to the ‘about’ file I have to go from the ‘index’ folder to the ‘home’ folder to the ‘about’ folder to the ‘about’ file.
When going from a file to the index page (or through a folder to another folder) for each folder you pass through you add a ../ eg: (using about files and folders) to get from the about file to the home folder you would use
about.html../home.html../index.html (at least I think that is the right way around)