This slideshare, “Basic concepts and principles of epidemiology” by Dr. Dharmendra Gahwai, is a lengthy but thorough and fairly accessible overview of the basics of epidemiology.
For a shorter and printable set of slides about epidemiology basics, check out this handout “Epidemiology: Basics of Study Design, Measures and Limitations” from Neal Simonsen at LSU Health Sciences Health Sciences Center.
You can take a web-based, self-paced course on epidemiology offered by the Centers for Disease Control and Prevention. It does not involve instructors, formal evaluation or CME, but the self-study course includes comprehension checks along the way. Start with Lesson 1 here.