Google Adsense is great, but you can't direct paste code on your site or HTML module. You can use IFrame Generator to generate code and paste the code into HTML module.
If you don't have a adsense account, you have to
Step 1:
Step 2: Wait up to 72 hours let Google to check your site.
Step 3: If you get confirm letter from google, then you can start to generate code.
After you sign in your adsense account
Step 1: click "AdSense Setup" tabs. There are three types product you can put on your site, AdSense for Content, AdSense for Search, and Referrals
Step 2: Generate code and copy the code.
Step 4: Filling width and height, click "Generate Code" button
Step 5: Copy IFrame code and paste it into your HTML module.