Hardware Secrets has posted an Introduction to Logic Gates

Logic gates are the basic components in digital electronics. They are used to create digital circuits and even complex integrated circuits. For example, complex integrated circuits may bring already a complete circuit ready to be used – microprocessors and microcontrollers are the best example – but inside them they were projected using several logic gates. In this tutorial we will teach you everything you need to know about logic gates, with several examples.

Introduction to Logic Gates