In Salesforce, you would need to create a connected application to get the API key (In Salesforce's term it is consumer key and secret).

Using this key a Shopiforce App can access Salesforce by its REST service.

In order to obtain Salesforce credentials you need to create a Connected App

In Salesforce go to Setup -> Under Build section on the left -> Create -> Apps -> New Connected App

Now you can click Save and that's all you need!

Now you should see this screen:

In Order to obtain Security Token please click on your username in upper right corner -> My Settings -> under Personal tab you will have Reset my security token. Once requested it will be sent to your Salesforce email address