There is no automated way to create an account on Earwigo. To get an account, you must first contact sTeamTraen (Nick) via the Geocaching.com website.
Note that Earwigo is not a “magic bullet” or a “Wherigo creation wizard”. If you have (a) never attempted to use the Groundspeak builder and (b) little experience with “computer stuff”, this may not be the right tool for you. Earwigo is intended to make the process of writing a cartridge easier and more reliable than the alternative, but it does not remove the need for you to understand the basic concepts (Tasks, Zones, Events, etc).
Once you've got an account, you'll be ready to Create your first cartridge