If you asking about adding html codes to your webpage, it's simply. Just put this html code in text editor (first click on icon Source). Clicking this icon once again is making you back in standard graphic editor (html code added there not working, you see only text). Save changes. This was about putting codes in mainpage or subpage.
You can to add this code in another parts of page too. Go to Edit design and you choose: Content of right box #1, or in Extended settings Content of right box #2, Text at top of page, Text at bottom of page or Text below the navigation (e.g. copyright). In this places you only paste your code, nothing more. Save changes.