Program a bot

For what i've done, there are some steps in bot programming:

First, knowing what you want to do, what your bot would be able to do. It can be one little action like fetching banana's price on any website you want.
Second, identifying the "support" of the bot, the platform it will be running on (Discord, Facebook Messenger, custom website...).
Third, choose a programming language. I would recommand JavaScript or Python for Discord, Ruby for Messenger. Just make sure there's an implementation of the platform in the language you want to use.
Fourth, think how you can actually do to create the bot (code-level plan).
Fifth, start coding! And if you get stuck, read the docs.

Hope it will help you do whatever killing-machine you want