Download and install dropbox, if you haven't already!
Open the My.DropPages dashboard and link your click "Sign in". This will give My.DropPages access to create a special folder in your Dropbox where your sites can live.
Click the "Create a new site" button and choose a domain name (e.g. my-great-site.droppages.com)
You're ready to go! Head over to the Themes page to download a ready-to-go theme and get editing.