Using telnet [on Windows] to see the HTTP protocol.

Linux and Mac (a variety of Unix) probably have telnet available
(in the shell, AKA command line "terminal").

[In Windows, start Command Prompt (cmd). 
Oh yeah, no menus in 8. Go to C:\Windows\System32\cmd.exe
Check if telnet is installed by typing telnet and Enter.
If not:
 Windows 7 and 8 need to have the telnet client turned on:

  Start | Control Panel | Programs and Features | Turn Windows features on or off | Telnet Client
]

Normally telnet is used to connect to a telnet server (listening at port 23):
(this is used for remote login, which we won't be doing)
  telnet IP_OR_DNS_NAME

But telnet can connect to any port (i.e. any server) 
by including an additional argument:
  telnet IP_OR_DNS_NAME  PORT
A web server will listen at the HTTP port (which numerically is 80).
Telnet can thus be used to connect to a web server 
and see the HTTP protocol in action:
Examples:
 telnet www.yahoo.com 80
 telnet www.asia.umuc.edu 80
 telnet davidwills.net 80
 telnet 192.168.100.101 80

[Unfortunately, Windows telnet will now blank out the screen
and not show what you type next! For how to fix this, see later.]

Once the connection is established (this uses TCP/IP, the Internet protocols)
you can send a Request to the web server with HTTP's GET command:
[on Windows you won't see what you type]
Examples:
  GET / HTTP/1.0
  GET /whatever.html HTTP/1.0
  GET /pathname/whatever.html HTTP/1.0
(follow the GET command line with a blank line)
[With the Windows telnet you will be typing these blind.]
The "HTTP/1.0" is the version of HTTP to be used; 
this all works better if it's included.
Capitalization will matter.

The web server first sends the HTTP "headers" as Name: value pairs
one per line, then a blank line, then the requested resource.
Example possible headers:
 Date:
 Server: 
 Location:
 Content-Length:
 Last-Modified:


Windows telnet stinks.
Let's use puTTy
On its configuration page, 
Host name: 192.168.100.101 
click Telnet button
Close window on Exit: Never 
Saved session: whatever  and then Save.