[zim1985]

When you use the Scanner to get user input, you usually (or I do at least) do something along these lines:

// Declare a new Scanner
Scanner input = new Scanner(System.in);

// Prompt user for input
// Use "print" so user input
// appears on the sane line

System.out.print("Enter some number here:  ");

// Use the Scanner class's
// nextInt() method to assign
// a variable the inputted value.
int num = input.nextInt();

I'm going to direct you to the Scanner class in the API as a guideline for getting other types of data.

Now for your conversion. The formula for converting from Fahrenheit to Celsius is:
Celsius = 5/9 * (Fahrenheit - 32)

Remember you are using floats, so your input might need to be in float format as well.

As for declaring variables, it really all depends on how much of the program you want to access it. For example:

public class Example
{
    // Class Scope
    int num;
    public Example()
    {
        num = 0;
    }

    public void exMeth(int num2) // <-- This only has Local Scope
    {
        int num3 = num2;
        // Local Scope as well
        // If you try to access these variables elsewhere
        // You will receive an error
    }
}

I hope that clears up some of your questions.

[MadScientist305]

The Scanner class has a method called nextFloat() which will read the next float from InputStream(System.In in your case). This method returns the float read, so you'd need to store that into a variable.

To do the conversion, you'd need to define a new method that takes a float as its input, and returns another float. In that method, you do the conversion. If the input is always in Fahrenheit, then you'd assume the input to the method is in Fahrenheit,convert it to Celsius, and return that value.

Regarding where to do all this, you need to get the input from the user after the "Enter a temperature" message, and once you have the user's input, you can pass that input to the conversion method you created.