Click "New connection" and finalize subscription. You'll see a product key. Copy it to the clipboard, you'll need it soon.
If you want to connect a public channel, skip this step.
If you're connecting a private channel, add Dilegram to it: click on a cogwheel next to channel's name -> Permissions -> Add members or roles -> check Dilegram.
Paste the product key you copied in step 2 (DMs with Dilegram).
Paste the product key there too.