Creating an app has become as easy as using a drag and drop builder. Apart from the planning and designing of the app, there is nothing much of a coding you will need to do. Creating an app, especially if it is complex with multiple options and pages and a full fledged client account to boot. You can try to consult and use another software for creating a prototype and test it, apart from that if you are wondering about UI and UX you can do so in no code app creators or Mockitt apps where you can design and plan a mock one for first hand experience.
Free app creators will allow creating apps, but what will make your app successful is the distribution. And distribution of apps is not free at all. Each of the app stores and play stores charge money for your app to be hosted on their stores. For this, Google charges $25 one time fees for Play store and $99 on Apple App Store yearly. These are only the hosting charges.
Have you received notifications about offers or updates about services from your favorite apps? This is another paid service that you will need to consider while buying a subscription plan for the app that you have created. There are pre-determined numbers of notifications for each month, if your notifications exceed this number there could be extra charges per notification.
Another charges are for the number of downloads during a month, your subscription has a particular number allotted for the downloads, whenever this number exceeds you will need to upgrade subscription or pay excess money. Each service could have different charges and you will need to check out which ones suits you the best.
There could be re-submission charges, white logo or no logo of the app creator charges, where you get to add your own logo. Add ons could also get you unlimited push notifications or unlimited downloads and editing. You could also get insights into analytics for better distribution of your app and insights into how you could monetize your app.
Whenever you create an app, it is better you create a comparison between several no code app creators and check out the one that suits you needs better.