What happens if you shot a gun in space?

The  fire cannot be ignited in oxygen-free space, but a gun can fire bullets into space, where modern ammunition has its own oxidizer, a chemical ignited by gunpowder, and can be fired anywhere in the universe even if it is not contain oxygen, but the shape of the smoke coming out after the bullet differs in space.

Imagine that you float freely in the intergalactic spaces, just you and your gun and one bullet, and then you fire this bullet what will happen?

Newton's third law: If an object a exerts a force on object B, then object B must exert a force of equal magnitude and opposite direction back on object A.

So According to Newton's third law, the force used to fire the bullet will generate other equal forces opposed to it. A few per second because your mass is larger than the bullet.

But what will happen to the bullet?

Don't wonder about the bullet's fate in space. The bullet will be in near space, making it stop completely after 10 million light-years.

But beware you may kill yourself!

Yes, you can kill yourself in space the bullet was fired horizontally when you are in the orbit of a planet where things revolve around it and which is in a constant state of free fall, it will orbit the planet to return to the place where it was launched. Where you can settle in your back!