In the Discord server of your choosing, click on the gear icon next to the channel you'd like to get your notifications in

Click on "Integrations" > "Webhooks" > "New Webhook"

Open the newly created webhook and click "Copy Webhook URL"

Go back to Slash, then click the "Webhooks" tab to the right of "Notifications"

Click "Create Webhook", and give your webhook a label, typically this is the channel name where the notifications will go to

Then go back to your notification preferences, and point the desired notification types to the webhook you just created.

Now, the webhook will send a notification to your desired server.