I started playing when I was nine years old. My dad played guitar, and he showed me the shape of a G chord. I also watched a 39-week series on public television called Folk Guitar. Mom and Dad recognized my interest and got the books that went with the series.
Beyond that, learning to play was a matter of playing every day, figuring out new things, and learning what I could by playing with others.
When people want to learn to play, I cannot stress enough the importance of playing every day, if only for a few minutes. You are already a guitarist. Playing every day helps you become a better one.