This is the easiest explanation I know for you to understand what affiliate marketing is.

A system of advertising in which site A (you) agrees to feature buttons from site B (them), and site A (you) gets a percentage of any sales generated for site B (them).

Another well known example:

Affiliate Marketing is a widespread method of promoting a website, in which an affiliate is rewarded for every visitor, subscriber and/or customer provided through his efforts. It is a modern variation of the practice of paying finder’s-fees to individuals who introduce new clients to a business. Compensation may be made based on a certain value for each visit (Pay-per-click), registrant (Pay-per-lead), or a commission for each customer or sale (Pay-per-Sale).

How can I learn how to implement affiliate marketing into my business?

Simply put – Rosalind Gardner

The Super Affiliate Handbook by Rosalind Gardner.  This is, in my opinion, the most popular and “learned” guide on Affiliate Marketing.  While it isn’t a classroom setting, this guide will empower you step by step with setting up a plan of action including how and where to choose affiliates in your quest for a successful affiliate strategy.  This affordably priced handbook is available here.