Greatest Integer Function

I am slightly confused about this greatest integer function.

For [[5.95]], the answer is 5 "...since 5 the largest integer which is less than or equal to 5.95."

Am I understanding this correctly by saying that the answer is the number in the unit's place. If that is the case, then the answer for [[3.66]] = 3, right?

The textbook tells me that "...negatives are a bit tricky. For [[-1.6]], the answer is -2 not -1."

Can someone explain why the answer is -2 not -1? Also, I need someone to briefly explain how this function is applied in real-life.

Is this function the same as the step function?

What is the easiest way to graph this function?