I am thrashing together an electric twin rotor. When I started I had a vague idea of how the things worked so I did some research.
The best site, although it's currently not being maintained, for model autogyro stuff is:
http://www.autogyro.com/ Read everything at the site, follow the links there, and you'll go forward with a lot more practical knowledge.
For a very good article on how 'Gyros work try:
http://www.jefflewis.net/autogyros.html
For ready-made rotor blades:
http://aerobalsa.com/
Basically, teeter and flapping are both ways of dealing with the retreating blade problem that affects all rotorcraft. A blade advancing into the airstream develops more lift than a blade retreating with the airstream. So one side (retreating) of your rotor disk is developing less lift than the other causing the 'Gyro to roll toward the retreating blade side. Visualize an airplane with one long wing and one short one. By allowing the blades to teeter or flap the effect on roll is minimized.
Teetering is where the rotors on a two-blade head are coupled together and actually teeter up and down on a pivot point at the rotor head. Flapping is the use (In models) of a flexible plastic mount for the rotors. They both do the same thing but flapping allows the use of three or four blade rotors.
The good news for you is that twin rotor designs don't suffer from this handling problem because the roll tendencies are cancelled out by the oppositely rotating rotor heads.
Hope this helps.