Some of both. I used to freelance, now I work for a company. Occasionally I do a freelance project on the side.
I also have some personal apps that bring in a residual (albeit small) income.
There is a lot of free learning information online regarding app development. I was in Touro for computer science and I watched a YouTude course in Android Development (called Marakana Android Bootcamp) on the side.
If you are interested, and the mods allow it, I will share some links to resources that I used.
If you are motivated and willing to work hard for it, you can be developing apps in 6-12 months.