Hello,
I have an app that I’d like to program myself. I know that there are different operating systems to program in, iOS/Android.
Can you please recommend how I’d go about developing the skills to build this, please? Is it covered in any of the Codecademy courses?
Thanks 
i would first learn the language required, and then go from there.
The tricky thing about building an app, is deciding upon the language(s)/framework(s). you can learn swift for ios, and java or kotlin for android. Which means multiple languages and two separate apps, or research hybrid solutions like react native (and many more)
@stetim, what are your thoughts on using Python as a coding language for building Apps?
Would you use Django or Flask?
App is such a broad terms these days, we have web apps, mobile apps. Which do you mean?
Web app? Depends. If I want to challenge myself and have all the time in the world, I would use Flask. If I needed to complete a project within a deadline, I would Django.
That is, if that those two (django and flask) where my only options.