linux distro's are mainly free operating systems for desktops pc's, laptops, home servers, web servers, business servers, etc, even supercomputers (over 90% of the top 500 supercomputers run linux in one form or another),
linux even runs on your phone - android is linux
linux is everywhere, you just do not see it,
some routers use linux, thin clients run linux, even arcade game systems run linux,
some top businesses, governments and their agencies run linux - such as the french police, even the us navy runs linux,
linux is highly customisable, you can do what you want with it because its free,
you can add, take away or modify it in any way you choose,
most software is free and available through the distro's repositories via the respective software manager,
i have over 10,000 pieces of software - all free and only a click and a password away,
you have probably already used linux cross-platform applications, firefox, vlc, virtualbox, audacity, avidemux, gimp, openoffice - to name a few,
its really not hard, my 9 year old daughter uses linux for youtube, facebook, homework, games, etc
have a look here and take the test
http://www.zegeniestudios.net/ldc/
i use this
http://www.mandriva.com/en/
there are free and paid versions, i use the free version
you are not tied into a contract as you are with windows and mac's,
most linux is free - totally free,
free to download, free to use, free to install as many times as you want, free to give away, free to throw it in the bin, free to change, free to modify, free to not use at all if that is your choice,
just free in all meanings of the word