I have just 'purchased' a virtual root server. I am new to all this, and I do not know how to set-up domains, install software etc. Will DirectAdmin assist me to do this?
yes, DA will help you do some of that. View the demo and read the docs mentioned above at sitehelper.
If you haven't visited WHT yet, check out their gigantic forum at www.webhostingtalk.com. There is a great deal of info about all of this.
Good luck!