The air will actually keep spreading out until it's like it's barely there at all. It will be the same number of gas molecules as before, but instead of being spread evenly over, say, a few thousand gallon volume of a spaceship they will be spread over trillions of gallons (actually much more than trillions, but you get the point).

A gas that isn't frozen solid or cooled to liquid temperatures will try to fill the entire volume of the container it's in, and out space has a huge volume. This happens because in gas form the various air molecules are all constantly moving and bumping into each other, so as they move they will spread out, because even if initially even if they were all moving in the same direction, eventually they would jostle each other and their motion would become random and they would travel in all sorts of directions.

At normal air pressure on Earth's surface we have 2.7*10²² gas molecules per liter of air (In chemistry in high school you'll learn that this is 1 mole of gas per 22.4 liters). We can have that density of air because gravity holds the atmosphere close to Earth and prevents the air from spreading out. This is why small planets don't have atmospheres, they don't have enough gravity to hold their atmosphere and eventually it all just flies away.

If you were in outer space and you exhaled, it would locally create an area with more air. However, because there are so few molecules everywhere else, this pocket of air will rapidly expand. You can think of it like the universe diluting your air. Because the pressure is so low in outer space (there are so few molecules close together), the expansion of this air is pretty violent, so you wouldn't have a pocket of air like you might see if you were to breathe into a jar underwater or something similar.

Space is a vacuum, which means a volume devoid of matter (without any molecules/atoms). However, it is not a perfect vacuum, there are a few (less than 100) molecules or atoms / cubic meter. This is roughly about 10,000,000,000,000,000,000,000,000 times less dense than air.

If you were to release air into this vacuum, it would very quickly diffuse outwards- forever. Soon the air molecules, mostly nitrogen and oxygen, would have spread out so much (because outer space is so big), that you wouldn't notice them, and the pressure would not change.

No, there will not be a pocket of air in space. Gases (like air) expand to fill their containers, and in space there is no container, so it would simply expand until it is the same density as space itself.

1. Interesting question! When you release some air into the vacuum of space, there will initially be a pocket of air. However, because of the natural tendency of molecules to diffuse, or go from a place of high pressure to low pressure (think about it like a bunch of balls on top of a hill; they want to roll downhill), the pocket of air will quickly expand. After a short amount of time the air will have expanded so much that the pressure can basically be considered to have returned to the original amount in the space (since there is so much emptiness).