I also recommend using for when you are learning and experimenting. It makes it very easy to try things out.
Also, in your browser, you'll want to use "developer tools". If you are using Google Chrome, this is a press of the F12 key away. You'll spend most of your time here in the "Console tab". You can try one-liners of code in there to get direct output. If you are working from a script, you can send output there as well using the following:
console.log('output goes here');
If you are using Firefox, you'll want to install Firebug for the same functionality.
If you are using Internet Explorer, you'll probably want to change browsers.