First if this is for outside of the internet, use illustrator, but illustrator has its limits as well. there are things photoshop can do that illustrator can't. Your question though was how with photoshop. I think photoshop is just fine if you are creating the logo for the web and web signatures. First, open a document the size you want the logo to be. I am not sure if you can do this in 6, but make sure the background is transparent so you will not have an odd white background to deal with on-line. Look for a tutorial on how to do this. You can use the shape tools to create the background for the logo and pick a color for it that you chose. You can also use the shape tools to make other shapes and the blends and filters to add effects. Check on line if you have a specific concept in mind- like drawing stars or other shapes for the logo. Also you can place a text layer. Once done you can create a merged copy to use on line and save for web, but keep your original to have and change later if you so chose. This way if you want to change the shape colors or text colors you can without having to re-do the entire thing. If you know the design you want, you can search for tutorials to help you achieve that design. Hope this helps.
search for Lynda tutorials for Photoshop... you will find for sure what you need ************************************************************