Probably to find your first user. Get feedback from them on your prototype. Startups aren't fungible so more info on your startup would help. Additionally there is a wealth of resources on the Internet: some of my favorites:

How to Start a Startup: startupclass.samaltman.com Watch the whole series, or you might regret it

Lean Startup: http://theleanstartup.com/ Get this book. If you're not a reader become one. Don't skim it; read it.

Founder's Dillemma: http://www.amazon.com/Founders-Dilemmas-Anticipating-Foundat... Read the whole book before you go get married to a cofounder