The graph in your problem is showing the position of the bus as time passes.
Think about how the position is changing as time moves on, or possibly over specific intervals of time.
Imagine the position line was going across the graph completely horizontally. That would mean the position isn't changing, so the bus must have no velocity.
Now think about if the position changed greatly over a very small period of time. Since the position is changing very quickly, the bus must be moving very quickly.
And remember that velocity is just speed with a direction. If an object is moving forward at 60 miles per hour, that object has a speed of 60 miles per hour, and a positive velocity of 60 miles per hour. If that same object is then going in the opposite direction (backwards) at 60 miles per hour, that object has a speed of 60 miles per hour, and a negative velocity of 60 miles per hour.
Is there a specific part of the problem you're having trouble with? With just the problem and no thoughts with it, it's a bit difficult to figure out where you're at!