Sunspots do not have any effect on the Earth in any significant way. If the sun was covered in sunspots, it could result in less light reaching Earth, but not enough to have any negative effect or even be noticed. However, magnetic anomalies associated with sunspots such as solar prominences, solar flares and coronal mass injections can eject energy particles that may affect power plants on Earth or satellites in orbit above Earth.
Sunspots are active, magnetic regions where the Sun's magnetic field ascends from underneath the Sun's surface and the particular magnetic regions break through. Sunspots are darker than the rest of the sun because they are lower in temperature and release less energy than the areas surrounding them.