The "Frequency Finder" web tool (and others of the sort) help you choose TV channels to operate within so you minimize interference from co-channel TV stations. If you're in an urban area, you may only have a small number of usable TV channels; if you're in a rural area, you may easily have 20+ vacant TV channels to pick from. In general, the TV channels with the most-negative signal strength (in dBm, on the right) are the ones you would want to consider using. The channels with protection above a certain threshold (adjustable by the Attenuation dropdown, where you can dial in the expected outside-signal attenuation based on the environment) are highlighted in yellow, meaning the program thinks they're usable. That's pretty much all you need to know to use the tool; the other information is there for more advanced interpretation.
Once you have that information -- what frequency ranges you can occupy without outside interference -- then you need to coordinate your wireless with each other, so you don't interfere with yourself. The tool I use for this is Sennheiser's SIFM. You would put in your existing wireless frequencies, the ranges you can use safely, then ask it to generate some number of additional interference-free frequencies.
While you might be okay by just selecting a preset, you might find that strange things happen when two transmitters are in very close physical proximity; they might interfere with another wireless channel. This is Intermodulation Distortion, and it's what SIFM and similar tools do the math to protect you from.
If you had just one or two channels of wireless, you'd probably be okay just selecting a preset and using it, but with 12 channels, you really need to coordinate. Especially if you're in a major market where there are no vacant TV channels at all.