If you look at what you've written so far. You have your Scanner import statement and then you create a scanner BUT you have them as comments so there not actually used when you run the program. Your first step would be to change that.
You then want the input value as a double so look here Scanner (Java 2 Platform SE 5.0)
And you will find a method for finding the next double.
You use this when you assign the value to your double, just as you have already done in your program but it will be = in.scannerMethod() the "in" bit refers to the name of the scanner object you created