Newbie question

Question – I already have a website someone else created. I hate it and want to once an for all do it on my own. Not wanting to shell out money for a program like Dreamweaver, a friend suggested I try WordPress. How do I create my new website using the same domain name and be able to work on it while my existing site is still up. Any information pointing me in the right directions would be appreciated!

Thanks!
Kerrie