Hi!
Sunspots are parts of the Sun's surface that are cooler, and so darker than their surroundings. They are cool because they are regions of very strong magnetic field, which suppresses heating there. The amount of strong magnetic field, and so sunspots, at the Sun's surface varies from year to year -- reaching a maximum every 11 years and then decreasing and reaching a minimum 5 1/2 years later.
cheers,
Sarah