As an Electrical Engineer (Comms, Sensors, and Systems), let me give the Electronics skill a shot...
Electronics-0 (Solder Jockey): The character knows how to change fuses, batteries, and cables; and knows that switching off the power first and back on last are important steps. The character also understands basic Arithmetic. No formal training.
Electronics-1 (Junior Tech): The character is familiar with component codes and placement; understands the basic concepts of polarity, phase, resistance, reactance and resonance; and can handle most derivations of Ohm's Law, Watt's Law, and parallel/series formulas. The character also understands basic Algebra, Geometry, and Trig. (Vo-Tech degree, average grades).
Electronics-2 (Senior Tech): The character can design build, and troubleshoot simple circuitry; such as cables, switchboards, gated logic, and operational amplifiers. The character also understands advanced Algebra, Geometry, and Trig. (Vo-Tech degree, top grades).
Electronics-3 (Junior Engineer): The character can design, build, and troubleshoot complex circuitry; such as receivers, transmitters, mixers, process controllers, displays, and sensors. The character also understands basic Calculus. (Bachelor's Degree)
Electronics-4 (Senior Engineer): The character can design, build, and troubleshoot complex systems; such as communications suites, entertainment centers, manufacturing facilities, safety/security systems, and medical diagnostic equipment. The character also understands advanced Calculus. (Master's Degree)
Electronics-5+ (Scientist): The character not only understands the theories behind all forms of electronics, he can invent a few himself. This type of person is called upon to investigate Ancient devices and enemy technology. (Philosopher's Degree)
Higher skill levels simply imply greater proficiency, as well as less skill in other areas (such as miscellaneous social skills).
The character's skill level also gives his proficiency with technical tools. Anyone, with a little practice, can handle a soldering iron. But which would you rather have work on your quad-core mobo, a "Solder Jockey" or a Senior Engineer?
(There, how's that?)