As mentioned at the beginning, Linux is not centrally administered. Because of this, there is no ``official'' release that one could point at, and say ``That's Linux.'' Instead, there are various ``distributions,'' which are more or less complete collections of software configured and packaged so that they can be used to install a Linux system.
The first thing you should do is to get and read the list of Frequently Asked Questions (FAQ) from one of the FTP sites, or by using the normal Usenet FAQ archives (e.g. rtfm.mit.edu). This document has plenty of instructions on what to do to get started, what files you need, and how to solve most of the common problems (during installation or otherwise).