If this is the first time you're connecting a store to Jilt, you'll be greeted with a prompt to select Shopify as your store's platform after signing in.
If you're adding an additional shop to your Jilt account, you can reach the platform selection by mousing over to the upper left corner of the screen. Then select "+Add a store" from the drop-down.
Click "My store uses Shopify". This prompts you to add the URL of your shop, and clicking "Connect" will link Jilt to your shop.
Shopify will ask you to approve this. Ensure that you're logged into the store you're linking to Jilt. You'll see this prompt:
When you click "Install app", the app will be connected to your Shopify store.