From Earth, we see the closest star to us, the Sun, every day. At night, you can see several more distant stars in the sky but they are a teeny-tiny fraction of how many stars exist in the universe. Believe it or not, there are five to ten times more stars in the universe than there are grains of sand on every single beach on Earth. The current rough estimate is that there are 10 sextillion (that's 22 zeros!) stars in the universe. There are 200 billion to 400 billion stars just in the Milky Way Galaxy alone.
Stars vary by mass, temperature, and luminosity, or brightness and can be put into categories based on these characteristsics. Most stars are smaller low-to-medium mass stars such as the Sun, which is a yellow dwarf star. The most common type of star in the universe are red dwarf stars which are cooler and smaller than other types of stars. The color of the star indicates its temperature. The hottest and largest stars are blue, medium-temperature stars are white or yellow, and cooler, smaller stars are red or brown.
High mass, or large stars, are called red or blue giants. Even bigger stars are called supergiants. The biggest of all are called hypergiants. The largest known star is a red hypergiant called VY Canis Majoris, which is 2,600 times wider than the Sun.
All stars are more massive than planets, which means stars have more gravity. If you consider all the matter (atoms) in our solar system, 99.8% of them are part of the Sun. The 0.2% of remaining matter is what makes up everything else--all the planets, moons, asteroids, comets, dust, and ice. This is why stars are always at the center of a solar system. Their strong gravitational pull is what holds planets in their orbits within the solar system they belong to.