Comes always in millimeter. Apparent field is marked in degrees. The manufacturer of the eyepiece give the apparent field in their technical data. Camera gives you the oportunity to choose the camera you want. Focal length is the distance from where the light is first bent till it meets in focus.
Magnification is by many considered as the most important thing at the telescope.
The magnification is rather insignificant, but is convenient for comparing preformance of different telescopes. Exit pupil is the diameter og the lightbeam that exits the eyepiece. If the exit pupil is larger than the pupil og your eye, you can manage with a smaller telescope. In most cases observing with less than 1mm exit pupil will not work. Field-size is maybe the most important thing of all.