Meet outside the front of the book store.
The book store can be reached by public bus (circulator) or by using the metro (union station stop) is the closest but still requires a 10-15 minute walk). A taxi or an Uber can also be used.
The tour will end at 7th and Pennsylvania St SE. You see Eastern market, a public market housed in a 19th century brick building and if the tour is on Sat or Sun between 9-4 pm you can enjoy artisans and food vendors that fill the streets.