First thing you need to do is think of how you want your site to look.
Do you want a banner at the top and 3 columns under it? 2 columns?
Where do you want the menu? On one of the columns? Below the top logo?
Basically, put it on paper. I usually make a rough sketch (i'm a visual person).
Once you know what you want it to look like, you need to make it happen. Do they have an editor that will do it for you? (While these work, they are not perfect and add code that's usually useless and can sometimes mess up your layout on other browsers).
What about the logo? Are you going to make one, do you have someone that will make it?
You can also find templates online but it's hard to find good ones.