Yes, tidal energy is abundant due to the thousands and thousands of miles of coast around the Earth. There is so much coastal land around the Earth that experience tides that the idea that there are few good sites is a bit silly. Technology may not be at the place to exploit all coastal sites yet, but nevertheless, the sites are there.
Tidal energy utilizes the flow and energy of the tides and currents to generate electricity. Because the tides and currents are driven largely by the gravitational pull of the moon, tidal energy is actually a form of exploiting lunar gravitational energy. There are different general categories of tidal power, although they both exploit the same basic tidal-lunar forces: tidal stream generators and barage tidal energy. Tidal stream generators are akin to wind turbine technology.