When you acquire app design knowledge, you can put that straight to work in a career as a mobile app designer, but also as a gaming designer, a graphic designer, an Android developer, a product designer, and other similar titles.
The most important part is that you take what you learned about app design and put it into practice. Start small with easy projects. Hack your way through early challenges and figure out what works best for you. Then, when you've acquired practical app design insights, you can level up your work to bigger and more complex projects.