Setup the app easily if you are using the latest have theme 2.0
1. Logging to your store, Go to the online store > Themes > Click on the Customize button.
2. Choose the page as "Cart" from the top of the header.
3. From the top-left side, Click on the "Add block" link and choose "I Agree To Terms Checkbox" extension.
4. Click on the "Save" button after setup the block. That's it!