A broken link means the server can't find the page you've designated in your link.  The two most common causes of this error are:

--The most common cause of broken links is case sensitivity issues.  Our servers are case sensitive.  That means that when they look at text an upper case letter (capital) and a lower case letter are two different characters.  To our server a and A are two different things.  So, if your filename is MyPage.html and you created your hyperlink to refer to mypage.html the server won't find it.  Check the values in your links against your page names to be sure the case matches.  You may want to get in the habit of naming your pages in all lower case all the time.  Then you know what to use when you specify your links.

Along the same line an error can be caused by spaces or other characters in your page names.  The explanation is long and complicated, but your best habit is to replace spaces with underscores _  and to only use letters and numbers in your filenames.  

--The file is in a directory inside of your web space and you didn't designate the directory when you created the link.  If you're using a web page creation program like Front Page, it should take care of all of this for you. 
But in case you're not, or in case you're program doesn't keep good track of these things let's look at how it works.  Let's say you had a help area on your website where you stored help files for your site visitors. 
And you created a directory named help to keep the help files organized and not mixed in with your other site files. 
And let's say you have a file in your help area called....oh, basic_help.html.  If you are on the main page of your site and you want to create a link directly to basic_help.html you would need to name the link /help/basic_help.html. 
If you just name the link basic_help.html the server will look for the file in your httpdocs folder where your index.html page is and not find it there. 
BUT, and this is where it gets tricky....Let's say that inside of the help folder you had a file named main.html. 
If you were editing this page and you wanted to create a link to basic_help.html you would just put basic_help.html in the link. 
Why??  Because main.html is already inside of the help folder.  So when someone click a link from main.html the server will start looking within the directory where main.html lives.....which is the help directory. 
AND, even trickier, if you are editing main.html and you want to create a link back to index.html.....you'd have to designate that link as ../index.html. 
The two dots and / tell the server to go up one directory and look there.