First, you have to go to the layout source. The layout source is the main html preview of the codes. Now, If you're already on the layout preview, right click anywhere on the page except in the areas where there are images. Click View Source on the right-click menu, and the codes will show up. Another way is by clicking the VIEW menu on the top of your browser and click View Source / View Page Source. That's it, now you have the codes.

You can learn how by clicking the How To Use Overlay Generator under Video Tutorials on the Menu. It will tell you all the details.

You can watch the video on How To Work on Addons on the menu. Click the How To Use Default Add-On under the Video Tutorials. It will show you in detail whatever it is that you want and have to know about the Addons.