There are many Linux distros to choose from. You may want to experiment with a few before you settle into one. I've been using Linux for 4 years and even though I have my favorite, I still try new ones frequently.

What are Distros?:
Companies package the Linux Kernel and thousands of GPL'd applications and distribute them to you (CDs, FTP, HTTP, etc..) so that you don't have to build everything from source code.

Packaging Systems:
A big difference between distros is the packaging system. Before packaging systems people would download gzipped tar files that contained either source code that they had to compile, or maybe pre-compiled binaries for their platorm. Packaging systems are a Linux equivalent to Install$hield (for the Window$ users). The packages contain smarts such as: library/software dependencies, content tracking information, install/uninstall scripts, etc..