If you're creating Web graphics, then there's no substitute for Save for Web & Devices. It disposes of non-essential data, reduces file sizes to their absolute minimum, and converts the image to RGB, the color space of the people.
Are you new to Photoshop? Have you been trying to teach yourself the basics of Photoshop but have found the amount of educational material available on the net a bit overwhelming?
This tutorial is demonstrating everything you will need to know about saving and presenting your work in Photoshop.