Read, search, try, learn, practise.
You can find web pages and videos, how to do simple coding. (C++, Java, python ...)
All coding languages have differences, so do SourcePawn
It is easier start coding with SourceMod plugins. https://sm.alliedmods.net/new-api/
You can look and read others dev's plugin source code.
You can make source file with simple text editor and compile plugin into server and test, see result.
This not sound nice advise but I suggest you to use more brain and not fall into too-simple-programs.
When I started practise, I only knew little bit <html> coding.
Now after ten years, I know little bit SourcePawn and <html> coding.
...or wait when somebody build that kind GUI-program.