Lets do this step-by-step;
Get The latest Firefox browser. Download it, Install it, and now open it.
Press Ctrl+Shift+k. A new docked pop-down window will open with Console selected by default. (Click on the image to view enlarged view)
You can enter a JS line in the bottom of the console window after >>>. Enter a line and press Enter. You will see the output in the large output screen just above. You can experiment by typing the following:
var somestr = "Your first JS Line"
1+1; //will output 2 in output string
console.log(somestr); //will output the string "Your first JS Line"
To print the output in Console window, you have to write the statements under console.log().
For example, console.log(1+1) in ScratchPad will give you the output as 2 in Console window. Simply typing 1+1 in ScratchPad will not give you the output in Console window. This is unlike the JS lines you typed in Console window itself after >>>
Try this code in ScratchPad and see the output in console window.
Errors in your JS code will appear in ScratchPad itself and not in console window.
You can always come back to this website to see my explanation of JS tutorials, in case you feel that the other resources are tough to understand.