What is the order from largest to smallest: galaxy, universe, star, asteroids, planets, moons, solar system?
From largest to smallest they are: Universe, galaxy, solar system, star, planet, moon and asteroid.
Let's describe them from smallest to largest. In fact the size order is not exact as there are exceptions.
An asteroid is a rocky body which lies in the asteroid belt between Mars and Jupiter. They are typically quite small object. The largest asteroid Ceres has been reclassified as a dwarf planet.
A moon is typically a rocky body which is in orbit around a planet. Some moons such as our Moon are quite large and are typically bigger than asteroid. Some moons can actually be smaller than some asteroids.
A planet is a nearly spherical body which is in orbit around the Sun. Planets are larger than moons.
A star is what planets orbit around. It is the source of light and heat. Our Sun is a star which is many times bigger than all of the planets.
A solar system is a star and all of its planets, asteroids, comets and other bodies. It is significantly bigger than a star.
A galaxy, such as our Milky Way Galaxy, is a collection of solar systems orbiting around a central core. Most galaxies have a supermassive black hole at their centres.
Galaxies also form clusters which are large scale structures.
The universe is everything. It contains billions of galaxies.