1. A tutorial will never teach you the whole programming language, it'll teach you the fundamentals/standards. Like anything else you learn from experience.
2. I believe so.
3. If you want to create GUI programs you'll either need to learn the native API provided for the operating system you are using or you can use something like Qt to create cross-platform programs. I only mention Qt since I use it personally, there are a bunch out there, just need to google them.
Thank you all I am actually 13 but always been learning and using computers since i was 3 so decided to learn a programming language since i know HTML and JavaScript so ill probably learn the tutorial from here then get a book then repeat process to learn windows API and when i have all C++ down ill go to learn some JAVA but thank you all!