Your bike's serial number is either located on the bottom of the frame, in between the two crank arms or below the stem on the front of the bike.
Be sure you write this number down and keep it in a safe place!
Register your bike/its serial number here:
http://www.vilanobikes.com/warranty-registration.html
If the bike is ever stolen, the serial number will be essential for law enforcement to (hopefully) recover your bicycle.