The only thing that a computer can store is bytes.

To store anything in a computer, you must first encode it, i.e. convert it to bytes. For example:

If you want to store music, you must first encode it using MP3, WAV, etc. If you want to store a picture, you must first encode it using PNG, JPEG, etc. If you want to store text, you must first encode it using ASCII, UTF-8, etc. MP3, WAV, PNG, JPEG, ASCII and UTF-8 are examples of encodings. An encoding is a format to represent audio, images, text, etc in bytes.

In Python, a byte string is just that: a sequence of bytes. It isn't human-readable. Under the hood, everything must be converted to a byte string before it can be stored in a computer.

On the other hand, a character string, often just called a "string", is a sequence of characters. It is human-readable. A character string can't be directly stored in a computer, it has to be encoded first (converted into a byte string). There are multiple encodings through which a character string can be converted into a byte string, such as ASCII and UTF-8.