where I should begin, and which free and reliable coding or app-?

where I should begin, and which free and reliable coding or app-development resources are available for beginners. I would greatly appreciate your suggestions.I am a PhD researcher and platelet biologist with a strong background in biomedical research. Although I do not have prior experience in coding, I am interested in developing an Android APK for research and educational purposes. I would like guidance on what foundational skills I need to learn, where I should begin, and which free and reliable coding or app-development resources are available for beginners. I would greatly appreciate your suggestions.