Next some basic terminology for the rest of the tutorial.
Each machine has it's own IP number. IP numbers function much like phone numbers. The are assigned in blocks to various institutions and companies by a coordinating organization, InterNic.
Within your lab computers can be interconnect via daisy chain (thick or thin ethernet), or via a central hub for token ring or twisted pair ethernet.
Campus interconnections can be through a mainframe - especially if security is paramount, through phone lines, or through a set of computers or controllers.
There are special controllers throughout the internet whose sole purpose is to get it all to move:
Routing is pretty close to sentient. Each router passes upstream the IP numbers it handles. They (the routers) pretty much do what's right. They even re-route paths when a segment goes down (at least in theory).
Routers are set up in a roughly heirarchical arrangement throughout the internet and communicate amongst themselves (using well defined standards) to move messages to the proper machines.
Even though the machines use IP number to communicate, people use names. The names are resolved by a heirarchy of name servers. NS.internic.net and it's "well known" name servers provide the top of the heirarchy. They handle name/number requests and direct the requestor the next lower server that handles that domain or IP range.
Communication is over some media (i.e. wire). It can be thick, thin or twisted pair ethernet, local talk, or fiberoptic (almost anything that passes the data). The information that passes over the media can have several protocols: IP, IPX (Novell), Appletalk, DecNet, or FDDI (100 MBit Fiber).
Inter-site transmission speeds are a factor of the phone lines and the equipment used. 300-28.8K baud can be achieved through normal phone lines and inexpensive modems. 56K baud uses a dedicated phone line and special communications equipment. T1 and T3 use groups of dedicated lines (24 and 96 respectively) to achieve higher rates.
This figure illustrates the Nation hookup or backbones. There are multiple major backbones and some rather complicated interconnection. It's not uncommon for your message to go from the east cost to the west coast and back again to get to its destination.