What does acceleration do?

To make acceleration equal zero. The velocity must be constant. For example, if velocity is constant at 10 m/s^2 its acceleration is zero. The same is true if velocity is 0 m/s^2.

You forgot to include something in your question, so it can't be answered.

Acceleration is the rate of change of velocity aka how fast the velocity changes

In the rotating frame, it can be (though it doesn't have to be). In a non-rotating frame, no (though it can be uniform in magnitude).

Yes, acceleration can be positive and negative because acceleration is a vector. It has both direction and magnitude. The direction is what makes it positive or negative. Negative acceleration is...