Sunspots are darker than their surroundings because they are cooler. Their strong magnetic field keeps some heat from reaching the surface (photosphere) of the Sun. Sunspots are much smaller than the Sun, but can be much larger than Earth. The link below shows the relative sizes:
https://www.windows2unive...re/sunspot_size.html
Here is another link with a movie made of images from the Solar Dynamics Observatory:
https://www.nasa.gov/feat...ot-turn-toward-earth