To get your Ecwid store embed code you can either use this guide or alternatively you can use the video below if you prefer visual guidance
Select App Integrations
And then select Third-Party Integrations
From here click the Add a third party integration button and find Ecwid in the popup that appears:
You should now see a field where you can enter the code from earlier:
After adding the code press back, this will take you back to your list of added integrations. Toggling the switch will enable the ability to add the store to your pages.
Navigate to the page you want to add the button to, and click the add a section button. You will be able to see your store under the category "Section Integrations".
Once you've added it to the page that you want the store to appear on click publish and it will now appear on your live site.