Hello Natalia C,

The instantaneous speed (the same applies to velocity) is like the average speed, but just for one instant of time. If you want to know the average speed (is it called so in English?) in a period of time, you can determine it in the geometrical way by linking with a straight line the beginn and at the end of this period of time in the graph of the function. Or you can do it the "mathmatical" way by dividing the difference in distance by the difference in time.

But the problem is that to determine the average speed this way you need to have two points. If you choose two points very near nearby, you will have approximately the instantaneous speed, but only approximately. If you want to know the real instantaneous speed, you will need to learn the derivations of functions. I am not sure whether this is calculus, but here on Khan Academy are videos explaining derivations of functions.

If you have any further questions or if I understood your question wrong, feel free to answer here! --Okapi

I think Okapi is right. You will probably need to learn calculus to find the instantaneous speed