Get A Bot
This is the first step in having your own telegram bot. Actually, come to think of it, the first step is for you to download telegram & install it. I'm not going to tell you how to do that - visit your app/play store & follow your nose :)
To get a bot you first start with opening telegram & starting a chat with @BotFather. All of the important stuff is discussed in the telegram bot documentation
Specifically, you want to use the /newbot command in your chat with @BotFather
Keep track of that token (you can get it from the Bot Father again if you lose it). We'll need that for the NodeRed telegram Bot.
The next thing that we'll need is your chatId