I could use some help with a stat that has become more and more popular the last few years.

Josh Lewin was talking about The Face's batting average against fastballs tonight.  How is a hitter's batting average against a certain pitch calculated?  If a hitter takes a 3-0 fastball for a strike does that count as an out?  Is a fastball that is fouled off calculated as a strike, therefore, an out?  If a hitter takes a swing at a fastball for the sole purpose of aiding a teammate who is trying to steal a base (not actually trying to make contact) does that count as an out?

Can someone please give me an explanation on this one?