First letís define bits and bytes. A bit is a single binary digit and can be a zero or a one. It is the most basic storage unit on the computer. A byte is eight bits and is the basic way of managing bits. Traditionally it took one byte to store a single character we use. However, as computers became international you could not store all characters of human languages in one byte so normally today it takes two or 4 bytes to store a single human character.
Memory and disk storage capacity is normally stated in bytes as they correlate closely to human characters so traditionally if it was said you have 100 million (100 mega) bytes of storage you could store about 100 million human characters. Of course, space for pictures are in terms of millions of bytes per picture so it really is not that simple anymore.
When information is sent across the Internet or thru our network it is put on a communications channel. These channels, whether telephone line, ether net cable, wireless, fiber or whatever work on one bit at a time being sent (although our bytes have been put in groups called packets or frames that have addresses on where to and from and more information) and then are received by the receiving device one bit at a time, Since it is only being sent a bit at a time speeds of communications are expressed as some number of bits per second (bps), today normally in megabits per second or gigabits per second. There used to be one exception to this rue and that was earlier printers often used a parallel port which meant there were 8 wires in the cable and they transmitted eight bits (or a byte) at a time. However today your printers use USB (a serial communications line) or serial cabling so work one bit at a time.