The common analogy is to think of the earth as a spinning top - it rotates about its access every day, but the direction of the axis wobbles in a circle. The result is that over time (a period of about 26,000 years) the earth's axis completes one revolution of the "wobble." This means that the north celestial pole wanders over that time - if you imagine the north pole extended from the earth into the celestial sphere the point of intersection wanders over the 26,000 year period, tracing a circle against the stars. Currently the north celestial pole is a position pretty close to the North Star, but over time that will change, tracing out a circle. As a consequence, the celestial equator also wanders against the celestial sphere - sort of like a hula hoop, it will tilt and rotate against the ecliptic because the celestial equator is always exactly 90 degrees from the celestial north pole. Hence if the position of the north celestial pole wanders, so too must the celestial equator. This in turn means that the point where the celestial equator crosses the ecliptic must also change over time. Remember, the ecliptic is the plane defined by the earth's orbit about the sun. The equinoxes are defined as the point where the sun on the ecliptic crosses the celestial equator; consequently the point of the ecliptic precesses. Just like the north pole. The solstices are the points of the ecliptic that are at greatest distance north or south of the equator, so they process as well. Hope this helps. Here's a site that gives a more formal description:
Precession - Wikipedia, the free encyclopedia
