This really is the best place to start.
If you are just starting out or are looking to solve a problem for yourself or for work I would recommend starting with an app builder of some kind. I’m assuming that you don’t know how to code ( I don’t ether) and you want to get your feet wet with learning how apps work. Back when I started I bought a white label subscription to an app builder called Bizness Apps. This tool really helped be build and publish my first app and learn how that whole process works. Later I developed a few apps with a tool called AppSheet. This tool is designed to help you build more of a data driven app. This tool is very powerful and with a little imagination you can build some really cool apps.
Give me some feedback on the types of apps that you want to make. Is it a Custom App or do you think you can build it with one of these tools?