A: It is a huge net with milions and milions computers connected with each other. (Are the perfect place to find lots of illegal porn,food recepies, bomb-recepies, secret government dokuments, and alot of nice old women to chat with. =) )
A: Well you need TCP/IP suport in your kernel. You also need a connection to an Internet-provider with an PPP connection or a SLIP connection or as a direct TCP/IP connection.
A: If you have a modem and a PPP connection you need pppd package and it should be configured with the scripts that comes with it. There is diald which is a program that dials to internet on demand. When an Inetprogram starts, the Diald-program just connects, and you are there. (where?) (here...) (Ahh!)
A: As internet is done with services you need to access them. For every service you need a client. As a user we are mostly use web access, ftp access, irc, archie, usenet, mail, telnet,... (see 6.0)