Now, the Image menu is here to help you in manipulating the color modes of your file and making general changes to your image.
If you're creating images for the web, your color mode should almost always be RGB. If you find that you can't apply certain filters or use layers, it's probably because your file is in the wrong color mode.
Going into all of the adjustment options would probably require a week. Suffice to say that here you can find all you need to manipulate the colors of your image. The most powerful adjustment option is arguably curves, which gives you full control of every color value in all three color channels.
Experiment as much as you can with the different options, because that is probably the fastest (and most enjoyable) way of learning how to use them!