Average And Instantaneous Velocity

What's the difference between average velocity and instantaneous velocity? 

Average velocity is the total distance traveled over the total amount of time it took. Instantaneous velocity is the current velocity of an object at a given point in time. 

How can I find the average velocity on a graph? 

To find the average velocity, first see displacement between where the object was at the beginning of the given time interval and where it is at the end of the given time interval. Once you have the distance, divide it by the amount of time it took to get there. For example, if an object moved 10m forwards, then moved 4m backwards, the displacement between point A and point B is 6m. If it took 5 minutes to get there, then the average velocity was 6 meters/5 minutes, or 72meters/hour. 

How do I find the instantaneous velocity on a graph? 

To do this, see how long the object was maintaining a constant velocity at the given point in time. Then see how far the object went while maintaining that same constant velocity at that same point in time. Divide that displacement by the amount of time it was at that constant velocity. For example, if an object started at 2 pm and travelled a total of 20 miles in 10 minutes and travelled 6 miles of that distance in 2 minutes at a constant speed, what is the instantaneous of that object at 2:01 pm? The object travelled 6 miles in 2 minutes while maintaining that speed, so the instantaneous speed was 6m/2min, or 3m/min, or 180m/h.