After you have registered as a partner, provided some details, and had your account reviewed, you can link stores to your account and start earning payouts.
To get started sign in to your partner dashboard and click on "Link New Store" on the left hand menu.
Select the application from the dropdown menu, fill in the myshopify address for the store, e.g. someclientstore.myshopify.com, and copy and paste the verification code from the embedded application interface.
To find the verification code, access the application interface via the Shopify Apps page, scroll right down to the bottom and copy and paste the code you see there.
Click "Save" on the "Link New Store" page.
Now, whenever the store makes a payment for the app, you will receive a share.