The Sun is very big compared to the Earth.   If you made a model to compare their sizes with the Earth being 1mm in diameter, the Sun would need to be 11cm.   The Sun is quite a big star compared to most stars.   The commonest stars are called red dwarfs.   On the scale of our model, red dwarfs are about 2.5cm in diameter.

But there are some giant stars that make our enormous Sun look tiny.   Betelgeuse ( properly pronounced betel (like petal) jerz (like the first part of  jersey) but its much more fun to call it beetle juice!) is absolutely unbelievably, colossally, huge.   In our model it would be 55m in diameter.   If you stuck it in the middle of our solar system it would span a distance of more than twice the Earth's orbit around the Sun.   So we would be deep inside it.  

 Despite being a long way away  (430 light years), Betelgeuse was the first star, other than the Sun, that astronomers managed to see as a disk rather than a point.   The Hubble Space Telescope image below indicates that the outer atmosphere of the star may extend beyond the distance of Jupiter's orbit around the Sun.   There is some radio telescope evidence that it could extend to the orbit of Saturn.  That would but its diameter at 2.7 billion kilometres!   In our model with an 11cm ball for the Sun we would require a sphere 214m in diameter for Betelgeuse.   To add to the amazing star's weirdness it is a very variable star, changes its visible brightness significantly over just a few years.   Researchers believe that the physical processes that cause this are making the  star pulsate, changing its  diameter by as much as 60%.

A Hubble Space Telescope view of Betelgeuse