A choice between two states
A bit, short for binary digit, stores one of two possible values: 0 or 1. Those values can represent any two-state distinction—off or on, false or true, low voltage or high voltage.
One bit carries very little information. Systems group bits together so they can represent more possibilities. With n bits, there are 2ⁿ possible patterns.
From bits to bytes
A byte is eight bits, so one byte has 256 possible patterns. Depending on context, a byte can represent a number from 0 through 255, part of a character encoding, a color channel, or one small piece of a larger value.
Unit capitalization matters: b means bit, while B means byte. Because one byte contains eight bits, 1 MB equals 8 Mbit when both use decimal SI prefixes.
How computers use bits
Processors use bit patterns for numbers and instructions. Memory and storage preserve bit patterns, and networks transmit them. The meaning comes from the format interpreting those patterns—not from the bits alone.