In JetForge admin panel go to Settings → Origins and hit Add Origin button. Select "Etsy" as type and name your origin (use your shop name especially if you want to connect multiple shops to single farm). Hit Submit button.

Now you are required to authorize JetForge with Etsy. Hit Connect with OAuth button. New window will open. You may be required to login to Etsy account. When login is completed, you will see prompt asking your if your want give access to your store. Hit Grant Access button. You're done!

Now you're able to import Etsy products and orders into your JetForge farm.