Hi,.
This is a very general question. It is answered many thousand times already.
I see nothing special in your post, thus we can't give special advice.
Numerous books, documents, tools, tuorials, videos....all available in the internet.
I recommend to do the "general" search on your own.
Decide what your goal is, what you want to do with the microcontroller.
( digital control, analog control or measurement, IOT, battedy powered, what display, memory, inputs outputs, interfaces...)
Look for similar applications, look how others did it.
Find out what item/way/solution you like...
Learn how to design electronics. Start with a clear requirement, with specifications ... a target.
*****
Then you will come to the point where you need help for a detail. You don't know how to achieve a requirement, you tried a circuit or a software, but it does not work like expected.....then we will be here to help you.
Klaus