True center or Core center?
True Center is the measured center of the ski (exactly half way between tip and tail) and may not be marked on your ski
Core Center is a little more complicated and varies from ski to ski, it takes into consideration flex, balance point, side wall height, and other factors, but is almost always marked on the ski (either as "center" or "core center" or even "recommended center")
But yes, you match up the mark on the boot with the marking on your ski and that's how you tell where your ski is mounted, it looks like this:
Always make sure you have the shop tech know EXACTLY where you want it mounted - especially if you want True center cause it's not always marked on the ski (and sometimes its slightly off), I usually measure and mark the ski before I bring it into the shop (just a line with sharpie on some masking tape) just so I know it's were I want it - I paid a lot of money for the skis and the bindings so I want it done right.
Hope that helps clarify it.