Input Incantations:

For input, at the top of your file, before the class but after the package statement, paste 

import java.util.Scanner;
As the first line inside the method where you want to read input, paste 
Scanner scan = new Scanner(System.in);
In order to read input from the user, we use scan, our Scanner
Here are some examples of using scan:
int x = scan.nextInt(); // read an int
double d = scan.nextDouble(); // read a double
String s = scan.next(); // read a String (no spaces)

If you want to read a whole line with spaces in it... 

String ss = scan.nextLine(); // read a String (works with spaces)

but watch out mixing this with the above.
For instance if you do nextInt then nextLine, and input "3[ENTER]" nextInt will accept the 3 and nextLine will accept the empty string with the [ENTER] (!)