I'd like to elaborate on this. There are basically three ways to specify a file path (the path to a file): relative and absolute. I don't know if those are the formal computer words for this.
If you want one document to link to something in the same folder (another page, an image, a stylesheet, etc.), you can just have its name within href or src. <a href="example.html">[/url], or <img src="picture.png">
If you want to link to something in a different folder, how you do that depends on where it is. If it's in a subfolder within the current folder, you use that subfolder's name. <img src="assets/picture.png">. If it's in a folder higher up, you can use two dots and a slash to say "go up a level". <a href="../index.html">[/url]. If it's in another subfolder of a higher folder, you can combine these path structures. <link rel="stylesheet" href="../style/main.css">
The other main way to do this is to always define your file paths relative to the main folder for your site. This is done by starting it with a slash, so <a href="/index.html">[/url] will always lead to your site's main index page no matter what folder the page you're coming from is in.
Writing links this way, the main index is always "/index.html" or even just "/" (i think), rather than sometimes being "index.html" or "../index.html" or "../../index.html", or however many more levels if you really love nesting folders.
You can also specify your site's address, <a href="example.neocities.org/blog/example.html">[/url], which means always typing out the longest form of the file path. I don't know a good reason to do this unless you're linking something on another site or another domain.