How to code a one webpage website?

How to code a one webpage website?

So i am completely new to web design and just recently was introduced to
html.
I found this webpage and tried to code it but i am struggling although I
know quite a bit about HTML.
Can someone please guide me through the steps, I want to make sure i am
doing things right.
At the moment I am struggling with centering the content area, which uses
an article tag.
This is the website so far
http://www.flickr.com/photos/100638499@N08/9557737748/ I would like to say
that i am not asking for someone to do this for me but to guide me if that
is not too much to ask.
This is my css so far
body {
background: url('index1.jpg') no-repeat center;
margin-top:300px;}
article{
background:white;
width:650px;
height:325px;
border:1px solid;
margin:auto;
}