Basically,
In photoshop you need to represent exactly how you want the website to look.
There is a slicing tool in photoshop which allows you to create areas in the design to be withdrawn. You can even select every area in photoshop! and save for web.
What i will say is this ia a very horrible way of making a website and can lead to disastrous speeds.
What you need to do is first work out how to create the basic layout and colours using HTML and CSS.
Find a valid HTML template you can use to start with and then add DIV elements to create boxes or areas which will be used to contain data or images.
Secondly use CSS to style and alter the DIV elements to a particular size or colour.
Once you have got the template as the general layout and it looks the same except without images and text, you then need to start bringing in the images and text. Meaning using photoshop slice the images and typing in the text in HTML.
If you need more information on HTML and CSS, the best place for learning particular information is:
HTML : http://www.w3schools.com/html/default.asp
CSS : http://www.w3schools.com/css/default.asp
Gary.