Learn programming languages like java for android, and swift and objective c for ios. To learn your own go to youtube and watch for free or you can also read blogs about app development. And the best option for you is that go to udemey and buy a best course about app development.
And if you need some help in app development or you want to develop an app then check out app maisters which is mobile app development in texas and they have very qualified texas mobile app developers. Check out website: https://www.appmaisters.com/app-development-houston/