I need help with some homework, there's a give away inside

Hey, basically I'm just looking for people who understand python, and can help me with some comp science homework, I'm sort of stuck, and normally I'm good at figuring it out on my own but this assignment is just wrecking me, and it's supposed to be "easy" I can figure out the hard shit but this string shit is killing me, I just want to know why and understand how it works right now so if you don't mind helping me out that would be awesome, I'm using processing, because I'm in beginner computer science, and that's what they use.

giveaway: https://www.steamgifts.com/giveaway/zigEF/neko-nin-exheart

By the way you're all free to enter, I don't really care one way or another, I just was hoping that someone would see it who had a comp science background and wouldn't mind me pestering them with a few questions.

Edit again: This is the problem I'm having trouble with:

First the assignment: For this question, you will write a program that allows the user to type in a number on the keyboard. When the user clicks the mouse, the program will calculate and display the square of the number that was typed in (e.g. if the user types in the number 12, then when the mouse is clicked, your program will display the value 144, i.e. 122).

This is the part I'm having a problem with:
When the user presses a key: Add any key that the user types to your string of digits. If the user presses a key that is not a digit, it’s okay if your program crashes (adding error-checking is beyond the scope of this question). Always display the current digits that the user has typed in using the text() function.