How to put a code that only activates on homepage

I have an ad pop up code but i dont know where to place it so it oly pop ups when users go to tetryx home. i tried adding it on top ad etc but it messes with the script. so can u tell me where to place it so it only activates on home?

Create a static html block with your code, set it active on the front page only (in the block's settings) and add its NAME (as !NAME!) in the front page template (in the "pages" tab)