First, upload the services app module and you can find Integrations -> Rest -> Chec; inside are lists of API methods I consumed (you can add more depending on your needs). Still, on the Logic tab you can click the server actions to see the 2 examples I implemented (please and more server actions depending on your needs, I'll keep on adding more)

Then go to the tab of your eCommerce app and click the manage dependencies icon, pick the Commerce.js API and check all its lists and apply. 

Fetch the Data into any screen you want to use it in;