Answer:
It depends on what browser you are using.
Here are ways for Chrome, Firefox, Safari, Internet Explorer, and Opera:
Chrome: Wrench icon (option menus) > Options > Under The Hood > Content Settings > Under the JavaScript section click "Allow all sites to run JavaScript"
Firefox: Click on the Firefox button (Tools for Windows XP) > Content > Click on Enable JavaScript.
(For Firefox you may have to open the Advanced menu and enable settings separately then just enabling JavaScript)
Safari: Choose Safari > Preferences > Click on Security > Click on Enable JavaScript.
Internet Explorer: Tools > Internet Options > Click on Custom Level > Scroll to Scripting section > In Active Scripting click Enable.
Opera: Tools > Preferences > Advanced > Content > Select Enable JavaScript.