The embed location for your Ad Unit code depends on the advertising format you choose.
If you are using a code editor, please refer to the following screenshot, a quick example of html page, to see where to paste the code for every Viralize format. 

Read below for details.

Video in Picture and Interstitial formats can be placed anywhere in your page. We suggest you place it after the <body> tag.

InText is a versatile format and can be placed at various positions within an article or blog post. Paste the code at the exact position that you want the player to expand from as high on the page as possible, so your earning potential will be optimized. You can try pasting it right after the <body> tag to make it appear within the header of your page.

Display must be pasted exactly where you want the Ad Unit to appear. If your site has dedicated ad or banner space, the Display Banner will adapt to the space allotted by your site’s template.

InStream formats appear in the form of a VAST tag, and require the Publisher to have his own player. Check your player documentation to learn how to configure the Viralize In-Stream/VAST tag.