From what I understand, you are trying to upload a reusable component, or a framework, compiled in a jar.
You cannot upload jar files, you have to upload the entire code (as Eclipse project or as Android Studio project or both).
To create a live preview for An Android lib, create a basic project using your component/lib, then create an apk for it and make it available as preview (either from your website or you can upload it to Google Play)
For previews, the same. From the already created demo project, take some screenshots to show to the buyer what he can do with your component (lib)
I hope that helps a it, if not, you can also take a look at how these authors (selling frameworks and libraries made it): https://codecanyon.net/category/mobile/android/frameworks-and-libraries#content