Once you are comfortable using Photoshop and are knowledgeable in the fundamentals of HTML and CSS, you will be able to produce basic websites.
- setting dynamic values in forms
- redirecting webpages
- displaying alert boxes and even accept user input
- rollover effects
Although buttons with rollover states is best implemented using CSS, more complex state changes and remote rollover effect is often more suitably implemented using Javscript.
There are also even timer-based events.