From ground zero, as Schlittenhund referred to, choose a distribution.
Begin at
Distrowatch. Package Management is what determines, for many, which distro is preferable. Myself, I like ubuntu-derived or Debian-derived or Slackware-derived distros (and not necessarily their namesakes) in that order. Perhaps do a search with "beginner" and "based on" as the criteria or just take time to browse.
Which distro can be somewhat determined by your hardware. Older machines with limited RAM and CPU speed benefit more from a limited number of so-defined distros. Modern machines with 4+ GB RAM and at least 1.6 GHz are not so limited. With the latter, 64-bit is the way to go, but with the former only 32-bit is going to work. RAM is the real limiting factor. Even modern machines work well with 32-bit distros if high performance is desired over appearance.
Other places to look are
SourceForge or
Softpedia. These have short descriptions associated with each distro listed.
Choices are so many that it is best to define to what purposes the user desires his device to be put. Ask which is the "best" and you will get almost as many answers as responders! It boils down to choice. Also, is appearance or performance more important
vis-vis the hardware? If you want both, then limit search to those distros with e-17, LXDE or XFCE
Desktop Environments.
TechieMoe has the best How-To on "How To Install Software In Linux." Check it out after a search!
Welcome to Free (as in both Freedom and Free Beer!) Open Source and GNU/Linux!