If the universe is expanding, how is Andromeda headed toward us?

Because the distance from the Milky Way galaxy to the Andromeda galaxy is so small compared to the size of the universe, the force of gravity overcomes/overpowers the force which expands the universe. This "force" is called "dark energy". If the Milky Way and the Andromeda were much further away from each other, dark energy would overpower the force of gravity between the two galaxies. I'm not sure of this, but I think this is why: the force of gravity is inversely proportional to the square of the distance (Google "inverse-square law"), but dark energy doesn't.

In short, the greater the distance between the two objects, the weaker their gravitational attractions, thus faster they speed away from each other. On the other hand, the closer objects are to each other, the stronger their gravitational attractions, thus the slower they speed away from each other. If the objects are close enough, gravity eventually overpowers dark energy and the objects head for collision with each other.

I think this is right.

Hope this helps! :)

The force responsible for the expansion of the universe is much weaker than the force of gravity. In terms of the universe, Andromeda and the Milky Way are very close, and their mutual gravitational attraction is more powerful that the overall expansion of the universe. Colliding galaxies are quite commonplace in the universe; the Hubble Institute published a set of portraits of colliding galaxies a few years ago.

Andromeda Galaxy

The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the Andromeda constellation. Also known as Messier 31, M31, or NGC 224, it is often referred to as the Great Andromeda Nebula in older texts. Wikipedia

Distance to Earth: 2,538,000 light years

Age: 9 billion years

Magnitude: 3.44

Stars: 1 trillion

Constellation: Andromeda

Apparent mass: ~1,230 billion M☉

Bro- you still got thousands of years. Don't worry you will be able to survive before it hits.

And when the universe expands, it refers to the outline of the universe. For example, if you blow a balloon, the middle in not impacted by its growth, only the outside is still expanding.

The gravitational force between objects decreases with distance, while the force of the universe's expansion increases with distance. Gravity is stronger than the force of expansion over short distances, but that is reversed over great distances. At some point, on the order of about 100 million light years, expansion overpowers gravity. That's a large enough volume for galaxy clusters and superclusters to remain intact, but beyond that they're expanding.

When a crowd of people leave a stadium after a game, does EVERY person have to separate from everybody else?

When a crowd of galaxies separate after the initial big bang, does EVERY galaxy have to separate from all the others?

The universal expansion and separation applies only at the level of super clusters of galaxies. Inside a super cluster (many thousands of galaxies), individual galaxies can and do orbit around each other, and sometimes combine.

All distant galaxies are moving away. The Milky Way, Andromeda and several other galaxies and dwarf galaxies that make up the "local group" are all gravitationally bound to each other.

It's due to the force of Gravity

its just a theory