As mentioned before and can't be emphasised enough, it's important to have an understanding of Mahayana first to see the appropriate context for Chan teachings. "Mahayana Buddhism: The Doctorial Fuondations" by Paul Williams should cover the basics. But there is a distinct teaching called Chan, although this becomes very confusing since in China (and Korea, and Vietnam) almost everyone is a Chan monk/teacher in a Chan temple/monastery. It's become a common name for anything Buddhism there. So, to find out what Chan actually stands for, can be tricky, as different teachers say different things. Hsuan-hua's Chan is not exactly like Sheng-yen's Chan, and the Chan of Hsing-yun (Fo Guang Shan) and Wei-chueh (Chung Tai Shan) are also different.
For an introduction to Chan, however strange it may sound, is Robert Buswell's translation of the works of Bojo Jinul (a Korean master), who combined the teachings of Zongmi (in English on his teachings of Chan see "Zongmi on Chan), Yongming ("Yongming Yanshou's Conception of Chan in the Zongjing Lu"), Dahui ("Swampland Flowers: The Letters And Lectures of Zen Master Ta Hui"), and the teachings of the Huayan school (Entry Into the Inconceivable: An Introduction to Hua-Yen Buddhism) in the book "Tracing back the radiance: Chinul's Korean way of Zen".
Or, if you are not yet up for intensive studying, and want to go to the essential things, there is this online book Chan (Chinese Zen)
(PDF) by Ven. Jian Liao. Another highly recommended and short reading are the few works translated
from Ven. Hsu Yun, especially his Prerequisites of the Ch'an Training
and The Ch'an Training