From the Site Checker section, choose 
HTML Validator.
Select View /Options... to open the Options dialog box.
Select Additional / HTML Validator to
make the settings for the HTML
Validator.
HTML version: Select the HTML version or the script file you
want to work with. For current browsers, version 4.0.1 is recommended.
Settings: Select the tags that are to be taken into account
while checking your website.
Quick Check: If you click the Quick
Check button, the default settings are restored. For example, the
Quick Check option removes invalid tags (elements), as well as "<"
and ">", i. e. single tags or empty tags, from the HTML code.
Click OK, to save your settings and to close the Options dialog box.
In the URL field in the toolbar, enter the
URL or file name to be checked. Make sure to include "file://"
for file names.
Click Start to start the process.
When the process is completed you find a list of all URLs including the number of errors and warnings on the right. These errors and warnings are displayed in the Details window.
If you click an entry, you find information about errors and warnings in the Details window. On the right, you can view and edit the HTML source text of the website.
If you wish to
save the report, click the Save report
button.