Speed refers to the rate at which an object travels. Unlike velocity, speed is a scalar quantity so direction does not matter. Average speed is calculated by dividing distance by time (e.g. miles/hour).
Okay we're going to talk about average speed, instantaneous speed is the distance that you're covering at a specific time. So 100 kilometers an hour, average speed is the total distance you're going to cover over a period of time. Okay this would be, well let's do an example, let's say we drive 150 kilometers in 2 hours stop for an hour, drive 150 kilometers in 2 more hours okay what is our average speed? Okay let's solve that, first we want to go our total distance which is 150 kilometers plus zero kilometers plus 150 kilometers over out total time 2 hours plus 1 hour plus 2 hours. So if we add up our total distance, we get 300 kilometers, our total time is 5 hours and we can simplify that, it's always good to simplify down to 60 kilometers an hour. Okay so that's an example of how you solve a problem or calculating the average speed.