Bot Framework Emulator is a desktop application that allows bot developers to test and debug bots, either locally or remotely.
ngrok is a cross-platform application that "allows you to expose a web server running on your local machine to the internet." Essentially, what we'll be doing is using ngrok to forward messages from external channels on the web directly to our local machine to allow debugging, as opposed to the standard messaging endpoint configured in the Azure portal.
Reference:
https://docs.microsoft.com/en-us/azure/bot-service/bot-service-debug-emulator