Ok, if you are completely new to web design this could be a steep learning curve, but I will try to help.
FTP access is a username and password that you use to get access to the files on your server.
In most cases the ftp url for your site is: ftp.mydomainname.com
This is provided by your hosting provider, so you will need to get hold of these details from your host. You can use a free programme such as Ace FTP Pro:
http://software.visicommedia.com/en/products/You need FTP access to access your DNN files and to download your skin files so that you can edit them.
Another way to download your skin files is to log in as host and go to the host menu / file manager click on the portal folder, open the skins folder and there you will see a list of the skin folders, hopefully you should see the folder for your skin that is installed on your DNN portal. - Here you can download the files to your computer for editing.
I always recommend that any skin creation and testing is done on a local computer and not the live site. I suspect that you will not know how to install your own copy of DNN on your computer for testing, so if you are going to be editing the live site be very careful and make copies of every single file you change.
You could start from scratch, but there is probably no need as long as you can get access to the required files.
You do have a skin.css file for your skin, I can view it from your main site, your skin is stored at:
so if you can get access via FTP or host access as mentioned above, navigate to the priceless folder as listed above to download all of the files.
Remember that you may not have a gradient image file etc. that is used in the tutorials as this is for a certain skin. Your skin will use different file names. - But the main elements such as a .ascx / .htm and skin.css files will be similar.
Hope this gets you started, thanks,