Links to an html file in the same folder (directory) can be simply inserted between the tags as filename.html .
If the file is in a different folder the code is more complicated. For every movement to a lower level add / before filename.html or folder name (but not when accessing a folder or filename in the same folder); for every movement up add ../
Consider the following folder arrangement:-
folder1------->folder2------>folder3
folder1------->folder4
folder1 has another folder4 in it as well as folder2.
Assume your html file is in folder2.
If the target file is in folder3 - directly below folder2 - the link code has to go directly down so the link will be:-
<a href="folder3/filename.html">
If the target file is in folder1 - directly above folder2 - the link code has to go directly up so the link will be:-
<a href="../filename.html">
If the target file is in folder4 the route is up to folder1 then down to folder4; the link code will be:-
<a href="../folder4/filename.html">
Play around with the options until you get it right.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.