Checkout UI extensions custom app

[a_zelinsky]

Hi, with checkout.liquid being deprecated, I need to move towards checkout UI extensions. I haven't developed a custom app before, and the disconnect between Shopify Partners and the Shopify store is confusing.

I followed scaffolding an extension step on the documentation, but am confused about how to move forward. I am able to see the app on my Shopify Partner dashboard. As this is a newly created Shopify Partner account, I do not see any stores under the stores tab on my Shopify Partner dashboard. How do I hook it up with the actual Shopify store, and run it locally to see changes? 

Thanks for your help!