The Sun appears bigger and brighter because it is much closer to Earth.
Step-by-step explanation:
Stars are the celestial objects, formed by collection of luminous body which is spherical in nature. Stars are formed by its own gravity.
Sun is also a star which is bigger in nature. Sun is present at the center of the solar system around which the planets revolve. sun is the main source of light and heat for all the planets revolving around it during day times.
There are also some stars which are bigger and brighter than sun but due to its presence in the solar system at the central position makes it closer to the earth. Therefore this is the main reason sun is bigger and brighter as it is much closer to Earth.