Well once you have your layout designed, you turn on Rulers if they're not on yet. Then use the guide lines to make boxes. Make a box around each image, each content area, and each navigation link. Then use the slice tool and make selections of each box. After you do this, every box that the guide lines make should be a sliced image over in your layers palette.

To save this for the web, go to File -> Save for web... Then the box should come up with the preview of your work. The only thing to worry about here is the file type you're saving it as. If it's a more simple site, not too extravagant, I would use GIF. But if you have a fancier design then save as JPEG.

Then another box will come up for you to name the file. Make sure you're saving it under HTML and Images. This way it will make an HTML document with the coding for you to customize and creates a folder with the sliced images. Then name it something like index.html.

Do you know HTML and CSS already?