are all stars bigger than the sun.

Answer

No. There are more stars smaller than the sun than there are larger ones. But there are some that are much bigger, and we see them quite well. The stars that we can see with the naked eye are usually larger than the sun.

By ‘big’ you may mean that they are large bulbs. How big a star is during most of its existence depends mainly on its mass (the amount of matter it contains). There are stars with up to 60 times the mass of the Sun, the smallest having less than a tenth the mass of the Sun. The heaviest are also the largest, the lightest the smallest. High-mass stars are much rarer than low-mass stars, which is why there are so many more small stars.

When stars reach their end (they run out of energy), they swell. Similarly, stars with rather small masses become very large late in their lives. The sun will then reach almost to the earth.