Most commercially available drones run on a frequency of 2.4GHz and or 5.8 GHz . The same as home wireless networks 2.4GHz.
Some higher cost models may use a sub-tone as well. This design is to reduce interference from highly populated areas with a lot of wifi signals.
Most operate LOS (line-of-site).
A jamming device would be a signal generator ( Voltage controlled oscillator, Power amplifier, saw tooth signal and noise generator, and a dc power supply to run it)
When the jammer is stronger than the operators controller or at closer LOS range, it interferes with the signal. Blocking or disabling the operators control.
This causes the drone to either return to its operator, or immediately land.
Because wifi is on this freq range. (2.433-2.5M MHz) It is not exactly legal in the US.
Lots of info available on how to and whats needed with a duckduckgo search though