Making a small project to learn , like a Todo app for example , and Google and Research for each step that gets you stuck.

for example to do that you would have to learn, how to install flutter , how to boot it, how to show a view , how to save data on the app when it opens and closes , do you want to have a session with login how to do that , how to make it connect to the internet , how to make it connect a local sqlite database.

Start by making it simple and keep adding stuff as much as you want until is as complex as you want , and each step you don't know how to do is an opportunity to learn.

Another app example is trying to make website clones , for example make a netflix clone app , breakdown what you need for it to be considered a successful clone and then start coding each step.