Start at:
http://x10hosting.com/panel.php
The login to your Cpanel. Scroll down, and the second to last row of icons at the bottom is "Software". Click on Fantastico De Luxe. On the lefthand side, click on "Wordpress", then just go through all of that and set it up! It takes less than five minutes.
Themes and plugins can be found for Wordpress with simple google searching. If you want to upload them, you will first need to extract them from the RAR file with 7zip or WinRAR (both free software). Make sure that each plugin or theme has its own individual folder.
To get themes and plugins onto your site, you will need to upload the files through FTP. I recommend FileZilla, as it is very simple and has easy drag-and-drop.
http://filezilla-project.org/
Basically, all you do is connect to the server (ftp.x10hosting.com) under the File menu (site Manager) using your username and pass for your account. Then you drag-and-drop your folders under /Public_html/wp-content/plugins or themes.
I hope that makes sense! If you need screenshots or more details I can provide them.