(1) are your eyes.
These are located on the front of your head, just above and slightly to either side of the protuberance called a nose.
These devices are used for observing the state of the capacitor. Often they will tell you things about the capacitor which may indicate failure.
Note that even if your eyes can't detect a failure in the capacitor, they are still required to properly use (2) and (3), so don't leave home without them.
(2) is a capacitance meter.
This is a piece of test equipment which measures the capacitance of a capacitor.
With this you can determine if the measured capacitance is close to the marked capacitance of the capacitor. Typically you need to remove the capacitor (at least 1 lead) from the circuit to use one of these.
(3) is an ESR meter. It measures the equivalent series resistance of a capacitor.
The ESR of a capacitor is often very important (most often in and around power supplies and regulators). It typically is an issue for electrolytic capacitors where this value can change over time as the capacitor degrades (as they do).
As the ESR rises, the effectiveness of the capacitor as a filter reduces. You need to (preferably) refer to the specifications of a capacitor (or alternately test a new one) to determine what a "normal" value is. The actual value depends on the type of capacitor, its value, the temperature, and many other things.
