A geek is someone who is always heavily into things like rpg, classic sci fi, and loves to argue about it with others or chime in any time they hear someone mention a geek Passion of theirs,whether appropriate to do so or not.
A dork tends to be a person who doesn't really look the part "aka wearing shirts like I'm not a geek, I'm a level 80 warrior" but they often have a love for gaming, in particular video games and team challenge with personal betterment online games. They may dabble in card and board games, again maintaining the temporary nature of an interaction (aka not lengthy involved games such as dnd) They don't usually run around talking to everyone about what they like but will engage if the other says something first.
Now either one can have a little of the other in them or even a little nerd. A nerd is just someone who knows an intense amount on a specific subject, tending to be but NOT limited to electronics and or computer hardware or software
n/a sentence example for dork,geek,nerd. Ya know em when ya see em ;)