You can add our ads to the theme (if you want them to be attached to a specific UI element or available on every page) or inside a post.
Adding ads to a Blogspot theme:
Navigate to Layout from the left-hand menu
Paste the code snippet into the 'Content' field and click 'Save'
If you would like to have a display or a Native Banner elsewhere (like the page header or sidebar), just drag and drop the gadget.
Adding the ads to a Blogspot post:
Switch to HTML view in the upper left corner
Paste the code snippet from the Websites page
You can also use a Direct Link — just insert it anywhere as a regular link.
Blogspot also allows you to edit the theme code directly, however bear in mind that it has some Blogger-specific tags which may not always be compatible with regular HTML. Adding your Adsterra ads via gadgets is more preferable.