NOAA
Noaa: National Ocean Service: Education: Tides and Water Levels
A great resource for explaining and understanding tides. Find out what tides are and why it is so important to monitor them. This is an extensive tutorial followed by a set of review questions. All of the information can be downloaded as...
Other
Physical geography.net: Introduction to the Hydrosphere: Ocean Tides
This is the last (18th) section of a textbook chapter on the hydrosphere. It explains what causes tides and tidal variations, describes some different types of tides, and shows on a world map where these tides occur. Includes link to a...
Woods Hole Oceanographic Institution
Whoi: What Causes Tides?
The Woods Hole Oceanographic Institute provides an in-depth but easy to read article on the role of the moon and the sun in respect to tides.
Other
Moon Tides: How the Moon Affects Ocean Tides
Discusses the different kinds of tides, high and low tides, lunar tide facts, questions people have asked about tides, and causes of tides.