When you install an app, app by default add section to all your themes. So if you wish to add zip code section to any part of homepage, only thing you need to do is activate it. Please follow these guidelines.
Demo link: https://rbz-section.myshopify.com/
Video Instructions:
Textual Instructions:
1. Go to App > Global Settings.
2. Change restriction type to be "Section (widget)"
3. Visit your stores admin panel.
4. Click on "Online Store" > "Themes" > "Customize".
5. From left side panel, click on "Add section".
6. Find and click on "Zipcode Restriction" and then click on "Add". Click back from theme area ("<" icon) which should take you to all sections.
7. Now you can drag and move newly added section (Zipcode Restriction) to appropriate location on homepage.
8. Click on "Save" and you should be all set.