In order to build a useful app you will either need the technical knowledge or professional services/a friend to help with the app. If you'd like to go with the first option I would recommend taking a look at NativeScript framework which allows you to use JaveScript, HTML, and CSS to build native Android and iOS apps. We have a lot of resources and tools that will help you in your journey. The technology is open source, some of the tools are fee and some are paid having freemium. You could get move information on https://www.nativescript.org/resources. You could also find some sample apps with open source code here https://www.nativescript.org/app-samples-with-code. Another place with sample code is http://www.nativescriptsnacks.com/.
Hope this helps.