>- confused about the fact that these machine has two different frequencies, i.e. 2.5 and the 30
The 30 kHz is the normal Clark frequency which is where you should start but it does not reach deep into the internal organs. The 2.5 kHz reaches the internal organs better.
>- also the red cable has had me confused.
The Red cable is positive and is the active cable. The reason that you should swap hands each time is to balance the energy. The signal from the red lead spreads across the body to a limited extent so that it covers everything between it and the green wire except the area immediately around the handle with the green wire. The signal also gets weaker in remote areas of the body such as the belly and legs unless you use the footpads.