how to automatically trigger a node-red flow by external app using the API
The external app can send to node red using HTTP, MQTT, Serial, UDP, TCP or web sockets. You could even use a Telegram bot. You will need to supply more info about your app and what protocols it can use.
it is bubble.io app please guide about http and mqtt how to create the flow
please give an example flow i can refer to
Do you mean you want to send a signal from your bubble.io application to node-red?
If so then where is bubble.io running and where is node-red running?
You first need to decide which method you can use to send from bubble. Can it use MQTT? If so then that might be the easiest.
If you want to learn more about MQTT then see this tutorial MQTT Essentials - All Core Concepts explained
yes i want this bubble is running online and node-red on local host
So first you need to find what methods bubble supports from the suggestions from @E1cid earlier. Once you know which one you want to use then the node-red end is not difficult.
[Edit] Ideally you want to use a method that does not require opening up ports on your router. Using MQTT with a broker on an internet accessible server would be a good way.
please tell using http in and email trigger
Look in the node red cookbook for examples on using http. But, as I said, using that method would require opening ports on your router, so you would also have to look at this FAQ post for advice on how to safely access node-red over the internet.
What don't you understand about using the email node.
As a beginner, I recommend watching this playlist: Node-RED Essentials. The videos are done by the developers of node-red. They're nice & short and to the point. You will understand a whole lot more in about 1 hour. A small investment for a lot of gain.
please tell hove to receive email by gmail in node red i want to trigger by email
I believe that you first have to setup your gmail account to allow that. If you search the forum for gmail I am sure you will find how to do it.