Gear ratio is the relationship between the size (number of teeth) of two gears meshed together for example, 1:1.5. The first number is usually the gear that the power is trasmitted to. The aforementioned figure tell us that one revolution of the primary gear or drive is equivalent one and half revolutions of the secondary gear pr for every one revolution of the primary gear, the secondary gear would've turned 1.5 times. The gear ratio can be simple calculated by looking at the number of teeth on the two gear wheels. It can also be calculated by dividing the tooth count of ring gear to the tooth count of pinion gear, carry out to 2 decimal point. The diameter of the gear wheel can also be calculated. The higher the gear ratio, the higher the torque.The term "reduction" is what you may also hear in conjunction with gear ratios and transmissions. Transmissions usually take the high speed (low torque) of the input shaft and reduce the speed to achieve a gain in torque, hence the name.
As for your seconf question, there's various types of EFis such as
TBI & CPI - (Throttle body injection) which uses a single injector into the throttle body for fuel delivery) while the latter Central Port Injection uses tubes to spray fuel (using a single injector) into the manifold rather than the throttle body.
Multi-port/Point fuel injection (MPFI) or Sequential port fuel injection (SPFI) uses one injector per port to spray fuel over the inlet valves, making for a more precise and accurate fuel delivery system.