University of Texas at Austin: Thomas Dillig's "Basic Lambda Calculus"
Read these slides, which will introduce you to lambda calculus. Skip the first 8 slides, which are about the organization of the CS 312 course. What are the four expressions in lambda calculus?
Click http://web.archive.org/web/20160726193758/http://www.cs.utexas.edu/~tdillig/cs345H/lecture1-6up.pdf link to open resource.