Mendix studio is WYSIWYG editor and mendix studio pro has lot more features compare to it. When you are starting with mendix you can go with mendix studio as it is beginner friendly. And then later change to mendix studio pro.
Mendix Studio- Perfect for Beginners and you can create very simple applications without any coding skills.
If are starting Studio then go through this learning path,
Mendix Studio Pro-Most of the development features are applied here.
These learning paths will help you to start on Studio Pro: