Hi Asad.
It takes time to learn programming, and in the case of Flutter, you have to learn everything about the mobile world of Android and iOS. There is no secret, look for tutorials or courses online, there are many videos and articles that explain how to use Flutter to develop applications. You can try looking for video tutorials on Youtube for example, or written tutorials. Don't worry if it costs you a lot at first, it's normal, as I say there is no secret; just work work and work. Be patient and as the years go by you will see that you will need to watch fewer and fewer tutorials to create your own applications.
Good luck.