(1st) pages 152-161 (Section 5.2.1-5.2.3), pages 165-172 (Section 5.3.3), pages 69-73 (Section 3.1.2), pages 80-83 (Section 3.2.2)
(2nd) pages 236-246 (Section 6.2.1-6.2.4), pages 251-257 (Section 6.3.4), pages 140-145 (Section 4.1.2), pages 152-155 (Section 4.2.2)
How the variables represent the data structure is captured by the (class) invariant. It is an assertion which should hold after initialization and which should be preserved by the operations on the data structure.
To visualize how Java objects are used to implement data structures like stacks and queues you may want to use the Java package explicar.