A string is an abstract bit of text. You need to encode this into a particular memory representation of the text.
Bytes hold a bunch of data in some encoding. It could be an image, UTF-8 or LZMA compressed ASCII. Once you know the encoding, to reconstruct the data you decode into a semantically meaningful form.
To put it another way, imagine the terms were "serialize" and "deserialize". Of course one serializes to and deserializes from binary data. Just replace "{,de}serialize" with "{en,de}code" and you're done.
