Margins and Padding Set
Computers and devices communicate on networks with electrical signals sent over a copper wire (like an Ethernet cable). Or, if wireless, they communicate with radio waves broadcast by mini radio transmitters.
At their basic level, all communications are electric signals sent over wires or propagated as radio waves. They are measured as voltages, normally in binary form (bits), either 1 or 0.
B. Physical Equipment
For wired networks, Ethernet is by far the dominate standard. It is a thin, twisted pair copper cable with RJ-45 connectors. The ethernet cable plugs into electrical connectors on the computers known as Network Interface cards (NIC), or now normally a built in chip.
A bridge connects different wring sections of a single local network. A router also connects two networks. The router is smart enough to tell whether the traffic is for the local network (in which case the router passes it on to the proper local address) or if the traffic has an address not on the local network (it which case it passes the traffic out to another outside router to which it is connected, and so on to its ultimate address worldwide).
C. Frames and Packets
Ethernet transmits data as frames containing a fixed or variable length of binary data (i.e., 1s and 0s, voltage or no voltage).
Most higher level networking protocols (on top of ethernet) such as TCP/IP transmit data as packets, which are also fixed or variable lengths of binary data (i.e., 1s and 0s, voltage or no voltage). Most computer networking systems are packet switched rather than circuit switched.