Go to the Settings section in the admin navigation and click on the Main Store Settings tab found there:
Click the switcher there to the "ON" postion, select your desired ZP page and click Save:
That's it! Your selected ZP page will now be used for your store's Homepage.
To revert back to using your original Homepage, just click the switcher to the "OFF" position and your original Homepage will then be used again.
*Note: If you change the "URL and Handle" of the page that is set as the Homepage, then your store's homepage will revert back to using your theme's original homepage. To use the ZP page once again, go back to the Settings within ZP, re-select the page and Save.
Once the "Use ZP page as the Homepage of your store" feature is enabled, we're replacing the code in the index.liquid file of your theme.
In order to preserve this file's original code, we're creating a new Snippet file called index.original.zipifypages.liquid (index.custom.zipifypages.liquid if the "use theme header/footer" feature is being used for the page) and placing the original code from the index.liquid file there:
Our code remains in the index.liquid file when the ZP app is disabled, but the previous code from the index.original.zipifypages.liquid or index.custom.zipifypages.liquid file will work instead, so your original homepage will be shown again when the app is disabled without any additional action required.
However, in order to get your theme files back to their original state (if you want to remove the ZP app from your store or otherwise), you just need to copy the code from the index.original.zipifypages.liquid file (index.custom.zipifypages.liquid if the "use theme header/footer" feature is being used for the page) and use it to replace the content in the index.liquid file.
Then remove the index.original.zipifypages.liquid or index.custom.zipifypages.liquid Snippet file and you're done!