A byte is a collection of 8 bits.
Bits can only be 1 or 0. If a bit is 1, then it is "on" or true. And if a bit is off, then it is "off", or false.
Because bytes are collections of 8 bits, they range from 00000000 to 11111111. And since each bit has two possible states, there are 8 of them, there are 82, or 256 possible permutations.
For example, 00000000, 00000001, 00000010, 00000011, and so on.
A byte was the perfect size for early computers. With 8 bits, it was possible to render ASCII characters like "%" and show up to 256 colors. But a byte was not so big that it was wasteful back when memory was really expensive.
These days we mostly use bytes to describe larger units of memory like storage. For example, megabytes (MB), or gigabytes (GB).
Note that the abbreviation for a byte or bytes is an uppercase "B". Bytes are often confused with bits, which are abbreviated as a lowercase "b".