Using Photoshop to create a web design is something almost all web designers do.. and is a skill that is needed to get anywhere in web design. Fist things first is that you need to have structure in your design and you need to have it that everything is the right size and can easily be sliced and diced to fit a css style sheet. To do this many people will use a 960 grid system which really help, using this grid system and keeping your design confined into the grid lines will ensure that everything is in proportion and when the time does come to get it ready to make it a actually full functioning website you can fast and easily. Fonts are the next thing you need to hmm... worry about, make sure that you use font families that can be used through css and are compatible with browsers, if you have any really unique fonts and really want them in your website design you are going to have to make them images I am afraid otherwise computers will not be able to read them. Make sure also that you keep to a theme when deigning you Photoshop website making it is creative but not to random otherwise you may find your website starts looking a bit out of place and hard to navigate. If you are like me you may find yourself spending hours on minute details which can be a waste of time.. make sure that you focus on the bigger picture and finish of the details later on otherwise you may never get everything perfect! You can easily test and view that your design is going to look like on internet explore by going file>save for web and devices you can preview your design in your browser there which will give you a really good idea of how it all looks and should look once completed. I hope this little summary of creating a website from Photoshop is at least a little bit helpful :D
Sorry if you dont understand everything I am saying I do apologize I come from Sheffield you see and I do talk as I speak like a yorkshiremen!