How do I identify an unknown component?

Short Answer: Use a combination of visual markings, multimeter tests, and context (where it came from and what it connects to).

Detailed: Unknown components appear in junk drawers, salvage boards, and mystery bags. Here's a systematic approach:

Component type	How to identify
Resistor	Color bands (axial) or numbers (SMD). Measure with multimeter.
Capacitor	Shape (cylinder = electrolytic, disc = ceramic), markings (µF, nF, pF), polarity stripe
Diode	Cylinder with stripe (cathode), two leads. Diode mode on multimeter → 0.6V one way
Transistor	Three leads, TO-92 (plastic) or TO-18 (metal can) package. Diode mode test between leads
IC (chip)	Part number printed on top. Search " [part number] datasheet"
Inductor	Usually green/blue epoxy-coated or toroidal (donut-shaped). Low resistance (1–50Ω)
Transformer	Multiple pins, copper windings visible, low DC resistance on primary/secondary
LED	Clear or colored lens. Diode mode → some glow dimly
Switch	Mechanical clicks, continuity test between pins when actuated
Connector	Physical shape, number of pins, keying features

The 3-step identification process:

1. Visual inspection — color, shape, markings, number of leads

2. Measure — multimeter (resistance, diode mode, capacitance if available)

3. Context — what was it connected to? Power supply? Signal path? Audio?

Pro tip: Search Google Images with "electronic component [description]" — visual matching works surprisingly well.