Tour meets in the Boston Common at the entrance to the Central Burying Ground Cemetery on Boylston Street. This is NOT the cemetery where Paul Revere or John Hancock are buried; that's the Granary Burying Ground down on Tremont Street.
For the Central Burying Ground Cemetery, if you're at the corner of Tremont Street and Boylston Street (where the Boylston St. T stop is on the Green Line)
you will see a Dunkin Donuts, turn right and walk down Boylston Street about 1/2 block, past the stone maintenance house (on the right), you will see a brick pathway that leads you to the entrance of the cemetery. It is across from the Barnes & Nobles at Emerson College and the Colonial Theater (106 Boylston St., Boston, MA 02116).
A parking garage is located on Charles Street (Zero Charles Street) between the Boston Common and Public Gardens.