The Internet is a large network of computer systems all connected together.
When you connect to the Internet you form part of that large network.
The Internet supports many ways in wich these computers talk to each other.
They use a standard called Internet Protocol.
This and all other protocols are decided by RFC (Refer For Comment papers)
In actual fact RFC's control the framework of how everything on the Internet must
work in order for the different computers to be able to communicate.

Every computer system has a number. Even whenever you connect to the
Internet your computer has a number, an Internet Protocol Number.
Other computers can find your computer and vica verca your computer
can find other computers with this number.
The number is written in four parts eg. 123.123.123.123 seperated with a
"dot" .
There is and Internet agency that allocates these numbers as they are needed.
This agency is run by the Internet Community at present although that might
change and be run by governments in the future.
The same agency also controls the allocation of TLD's (Top Level Domains)
eg. .com .za .gov .net .org etc. etc.
More about that in the Domain section.