every computer which is "connected to the Internet" has a
unique 4-byte identifier. This is called its
IP Address (of which we shall see
much more later on),
Big Idea #2
when data to be delivered across the Internet, it is first
diced into small(ish) units called packets. A
packet consists of two parts: a header and a
payload. The header contains (among other
administrative stuff) the IP address of the packet's
destination.
Big Idea #3
the Internet consists of many, many Interconnected
Networks -- hence the name! Networks are connected to one
another by special-purpose computers called
routers.
When a packet is sent "into" the Internet, it passes through a
"local" network to the first router -- sometimes called a
"gateway". This router examines the packet's destination address
and decides which router, of all those it is directly connected to,
it should forward the packet onto for its
next hop. The process is repeated at the next
router, and so on, until the packet reaches its destination.
The definition of how this all works, the format of packets, how
routers behave, etc, is defined by the Internet Protocol
(IP). In general, a protocol is a set of rules together
with a set of data structure definitions (the packet formats) which
define how a set of operations (in this case, Internet packet
delivery) is carried out.