Before you can write any sort of code, you'll want to have a tool that lets you edit your AddOn files. However do not get overly distracted with the tools themselves while trying to get your first AddOn created. Any text editor, like Windows Notepad can edit the files. All AddOn files are plain text files. The editors can make the coding and many repetitive tasks easier for day to day editing, but it's often very difficult to learn the tools and try to learn the AddOn at the same time.
Anyway I will go ahead & download the Twitch app like everyone's saying, but I still need to know whether my in-game addon settings will carry over automatically, or whether they'd return to default same as if they'd all been uninstalled in the curse client then reinstalled from scratch. Because if it's the latter then I will have to take screenshots of the settings on all my toons BEFORE I install the addons thru the Twitch client.