First take the downloaded .zip file and place it in whatever directory you might like to keep it in. This could be in your "Documents" folder. Next right click on the .zip file and choose "Extract All...".
chassis-1.png
You will now find a file with the title of the manual you have downloaded and a "files" directory. Click on the file with the title of the manual.
chassis-2.png
This will load the first navigation page into a browser window.
chassis-3.png
You can now use these links to navigate the manual.