Page 126. " My people "
slavery
Public Domainslavery - Credit: Dittaeva: wikipedia
Dr Copeland is referring to people who were brought to America as part of the Transatlantic slave trade. From the 16th to the 19th century, Africans were captured and brought to the New World to work on plantations and farms. Blacks were routinely considered inferior in America even when freed from slavery. 
Page 128. " John Brown "

John Brown was a passionate abolitionist in the first half of the 1800s. He led various attacks on pro-slavery individuals and was finally hanged for inciting riots and attempting to arm slaves. 

    

Page 135. " He had a tabernacle and preached every night "

In this context, a tabernacle is a temporary or portable building for worship. 

Page 140. " Smoking reefers "

reefer
Public Domainreefer - Credit: Erik Fenderson
A reefer is a cigarette made from marijuana. Marijuana or Cannabis is a plant, the dried flowers and leaves of which can be taken as a recreational drug. Effects of smoking or ingesting it include an increased heartbeat and a general feeling of well-being and relaxation.

Page 141. " Three squares and a flop "

Three (square) meals and a place to sleep.

Page 141. " D.A.R. "

The Daughters of the American Revolution is an organisation made up of women who can prove a direct lineage to someone who played an active part in achieving the independence of the United States. They work as a charitable organisation, promoting historic preservation, education and patriotism.

 

Page 143. " She and Bubber played Parcheesi "

parcheesi
GNU Free Documentation Licenseparcheesi - Credit: Micha L. Rieser
Parcheesi is a board game. A version known as Ludo is available in the UK. The rules involve shaking dice and moving all your pieces to the centre space.  

Page 144. " She wanted to learn how to read music already written down "
sheet music
Public Domainsheet music - Credit: Tkgd2007: wikipedia

There have been various forms of musical notation at various times and in various cultures, but in the Western world musical notation is now standardised. For piano, music consists of two staves (the two horizontal rows of lines) and each line and space on the stave represents a note. The top row is the treble clef and represents the higher end of the keyboard, notes that will usually be played with the right hand. The bottom row is the bass clef, lower notes usually played with the left hand. The shape of the note on the clef describes its length. Other symbols represent pauses, the manner in which notes should be played, and sharps and flats.