I'll try and take this from the top..
MM is just how far you are 'zoomed' in.
Imagine you stand at one fixed point and point your camera at a person standing 10 meters away.
A 14mm len will reveal everything around the person and the person will appear small. A 35mm lens will be closer, but still quite wide. Say for example you switch to a 200mm lens, you will get much much closer and probably cut the person off at the torso. Now, MM's are not everything in the lens world. The 'real' MM's are always connected with your sensor.
We are getting quite technical here, but the cameras you mentioned (t4i and 60D) both have an APS-C sensor. Another camera, for example a 5D has a Full Frame Sensor. A GH2 has a 4/3rds sensor.
Easy way to show this:
Canon EF 50mm F1.4 lens
Full Frame Sensor: 50mm
APS-C sensor: 80mm (An APS-C sensor is smaller than a Full Frame, thus the focal length becomes longer. Multiply by 1.6)
4/3rds sensor: 100mm (A 4/3rds sensor is smaller than APS-C and Full Frame. Focal length becomes longer. Multiply by 2)
Now, this is just a little thing about lenses covered. What you asked basically. There is a lot more to lenses, but we are becoming more technical by the minute. It's stuff to learn later on.
When you ask about Cinematic Mode, I think you just want your image to look cinematic, like in most films.
It's not a mode you switch on. You get a cinematic mode by combining a few different settings.
Your camera settings matter and also your lens. This is just capturing from the camera point of view. Lighting is what makes your image cinematic. Colour Grading is the final touch.
Quick Camera Setup Guide:
Most of the time we shoot: 24p (Camera takes 24 pictures a second), 1/48th shutter speed (Double of what your frame rate is). Then there's stuff like ISO, which controls how bright your image is. Aperture is what is adjusted on the lens. The lower your F-Stop, the shallower your depth of field will get (your background will be out of focus/blurry). Often an out of focus background is considered cinematic. It is very helpful to shoot with a blurry background if you want to focus your viewers attention on the subject you're showing.
However, as mentioned before, a DSLR might not be perfect for shooting a documentary. There are many problems with DSLR's, especially Audio, Rolling Shutter (Jello effect in your image) and much more.
If you have the money, a Sony EX3 or EX1 would be great for documentary stuff. They're not too expensive and are good cameras for the documentary genre.
There is so much to know about cameras and there are so many cameras out there.
The thing you have to know is, there is no 1 camera for every job. You choose different cams for different jobs. In the end, it boils down to your story telling, composition and lighting! Not to forget sound. A film is nothing without the right audio!