These are links for the introduction to Reformed Theology which are in my opinion the best available on the web.
New to Reformed Theology? Here’s Where to Begin.
New to Reformed Theology? Start here.
What Is Reformed Theology? by Dr. R.C. Sproul (video series)
What Is Reformed Theology? by Dr. Ligon Duncan (video)
10 Things You Should Know about Reformed Theology by Dr. Joel Beeke and Dr. Paul M. Smalley
Introduction to the Reformed Faith by Dr. John Frame
Reformed Theology Is Covenant Theology by Dr. Richard Pratt Jr.
What Is Reformed Theology? Understand The Basics by Dr. R.C. Sproul (pdf)
What Is Reformed Theology? Its Roots, Core Beliefs & Key Leaders by Dr. Daniel Hyde
The Reformed Faith by Dr. Loraine Boettner
Reformed Doctrinal Distinctives by Dr. Greg Bahnsen (pdf)
A Brief and Untechnical Statement of the Reformed Faith by Dr. B.B. Warfield