Sunspots:

The sunspots are the most conspicuous feature on the photosphere of our Sun. It was Galileo who first showed that sunspots were actually surface of the Sun itself and were not connected with the Earth or other planets in any way. Then for centuries after Galileo, it was believed that these dark spots were holes in the Sun through we could peep into the supposedly cooler interior. Even the famous astronomer, Herschel conjectured that the Solar interior might be cool enough to support light .If big enough, Sunspots can be seen with the naked eye, particularly when the Sun is quite low near the horizon or shining through dense mist or fog. However, such naked eye identification of Sunspots is vaery rare.
It is now known that the Sunspots are the regions of relatively less hot photosphere. At the Sunspots, the temperature is about 4500 degree K compared to the temperature of the average photosphere which is 6000 degree K. By observing the day to day movement of Sunspots on the face of the Sun, one can directly demonstrate the rotation of the Sun about its own axis.

Image:Sunspots
Source: SEDS
Credit:Bill Arnet
Visit:
http://www.seds.org/nineplanets/nineplanets/sol.html

At the equator, the Sun is found rotating about 25 days and near the polar regions, the rotation gradually lengthens to about 34 days. So an average we can say that the sun rotates on its axis once in about 27 Earth days,(revolution period of the Sun around the center of the Milky Way Galaxy) is of about 220 million days.
The Sun's rotational axis is slightly tilted; the plane of revolution of the Earth, at an angle of 7 degree 15 min, so that the Sunspots appear to move across the Sun's disc at varying directions at different times.

It is seen through records that the Sunspots number varies from year to year. They increase towards a maximum and then fall away to a minimum during the following years - The Sunspot maxima occur once every 11 years, although the maximum number of spots and their latitude distributions vary during each cycle. Each 11 years, Sunspot cycle begins with the appearance of spots at latitude of 25 to 30 degrees. Spots disappear and new ones appear at lower latitudes, spota re very rare, about 45 degrees North or South and on the Equator itself.
Associates with each spot is a magnetic field that behaves as if a long bar magnet had been inserted into the spot with one end sticking out. The pole of this apparent bar magnet seems to revers every 11 years, so that the same magnetic polarity associated with the spot activity returns every 22 years.

Image: Sun Spots
Source: http://www.astronomynow.com/index.html

The center of a Sunspot, being dark, is called the umbra of the spot. It is surrounded by the penumbra, which is obviously brighter than the umbra but still not as bright as the photosphere. Sunspots are dark when compared with the photosphere which is indicative of a lower temperature, this fact is verified by spectrograms made of sunspots. But the Sunspot is not black in any sense of the word. It is dark only when compared with the photosphere, because its absolute temperature is about one quarter less.