I have put some questions in your code. Answer those for me and I can help you from there. Who knows, maybe answer those questions will clear some things up for you while you answer them.
Also, please put your code in java tags. Read my signature to figure out how.
Here is the commented code, please answer these questions for me and we can proceed from there:
public static void main(String args)
//This is a variable that you immediately garbage collecting
//Why do you have the previous line if you have this?
Scanner input = new Scanner(System.in);
//Why a float?
System.out.println("Enter a number.");
//Where do you get the number the user enters?
System.out.println("Select 1 for square or 2 for cube: ");
//Is this supposed to be 1 or 2 or the number the user entered?
square = input.nextFloat();
//Why greater than or equal to 2?
//Why multiply by 2?
//Why didn't you finish this line of code?
System.out.println(square + "