Resistors (Ω) oppose current, are color-coded, and connect in series (Rt = ΣR) or parallel. Current-limiting resistors protect LEDs.

As explained by Arduino to Go, each color band on the resistor corresponds to a number but this can differ depending on the band's placement. It's not complicated, but the sheer number of colors ...

Example: a resistor has a stated value of 100Ω and a tolerance of 10% Calculate the tolerance range 10% of 100Ω = (10÷100) × 100Ω = 10Ω Determine the minimum and maximum resistance values: ...