I don't know for sure for M&T stadium, but so far in this tour, parking has always been separate than the tickets. Unless you bought a VIP package or something like that in which you should have received a separate parking pass in your package.
EDIT: On the stadium website, it says parking is $15 (that is pretty cheap!)
Closer to the date of the show Ticketmaster or LiveNation usually sends an email about venue information such as what time the lots will open up, where to line up for General Admission, etc. If you bought your tickets from external sellers instead of Ticketmaster, keep checking the
M&T Bank STadium website for posting of information.