This is going to be extremely cliche but experience. I want to say my dad, but really I learned most myself by trial and error, and exploring, research, saying "**** it, lets try it", ect.
I started my computer experience with a Commodore 64 and after that my dad allowed me to play on his PC which was a 386 based DOS 6 machine. I was 7 years old. In 99 when we moved and got a bigger house I got my first desk which confused me because all I had at the time was NES/SNES/N64/PS1. Turned out I got my first PC which was a Pentium 1 based machine with Windows 95. My dad looked at me and said, have fun, you wont break it. Took me a while to grasp the concept but wasn't really interested in computers until around 2002. I'll take the time to mention my dad had a degree in electronics engineering, was an electronics/audio/car nut, and had been playing with computers since they had tubes in them. I discovered the internet kind of "late" for that period only because we didn't have a home phone or dial up. By using the internet at school I discovered through it and my dads friend how to hack WEP and all about wifi and long range signals and antennas. Consequently I found some poor soul in our area with a WEP router and Direcway (now Hughes satellite internet). That is when I started getting into PCs. I "acquired" XP Pro and went to town. It's history from there. Just a ton of experience as I had no real friends so all I did was sit there and mess with things. Even today I'm always experimenting with things. Whether it be with new OC settings or trying to discover new things to do to my 98 box. I like to play with old and new hardware to pass the time while watching my son. Because of all this I'm a reviewer on another website and I think I might be taking over a co-workers tech article. That may or may not happen.
It also helps that my uncle is also into tech but not to the extreme that I am. Though I did get quite a few good video cards from him over the years. Voodoo 2 SLI, Voodoo 5 5500, Geforce 2 Ultra, Geforce 3 TI500, Geforce 4 TI4400, Geforce FX 5600Ultra. Just recently he gave me a huge box of stuff (like, 4 months ago) that had a random Q8200 and 2 Gigabyte 775 boards in it.
It also helps that I stay up to date on the latest tech, memorize benchmark numbers, and try to have a list in my head of what is better than what with what price.