Tau, charge times and the filter cutoff from a resistor and a capacitor.
A capacitor charging or discharging through a resistor follows the time constant τ = R × C (seconds, with ohms and farads). After one τ it reaches about 63% of the final voltage; after five τ it's over 99% - effectively fully charged. The same pair also makes a simple filter with a cutoff frequency of f = 1 ÷ (2π × R × C).
Type values the way they're printed: 10k, 100n, 47u, 2.2u.
10 kΩ with 100 µF gives τ = 10,000 × 0.0001 = 1 second: about 63% after 1 s and fully charged after 5 s. As a filter, 10 kΩ and 100 nF cut off at about 159 Hz.
RC timing sets power-on delays, soft-start, reset circuits, relay and speaker-protection delays and oscillator frequencies. If an amplifier's speaker relay clicks in too late or never, or a supply starts slowly, a dried-out electrolytic capacitor in the timing network is a prime suspect - its capacitance falls, and so does the delay. Replacement capacitors are in our parts catalogue.
Circuit Fixers has photos of real circuit boards from repairs with every component marked - find your device and see what each part is and where it sits.
Search the board library Parts catalogue