Is there a library or something that I can import for Processing which can show a GUI box which prompts the user to fill out information, for example age, gender etc?
g4p, control p5.
Which one should I use or is easier to use?
Go for g4p please
It’s a matter of taste
If you want to show your GUI on top of your sketch maybe select ControlP5. It’s easy and commonly used. I developed a library called UiBooster, which creates dialogs in separate windows. It’s also very easy to use:
String opinion = new UiBooster().showTextInputDialog("What do you think?");
It’s up to you. Select want fit your needs.