Whats the difference between speed and velocity?

Although these two words can be used interchangably they are very very different. Its easier to explain if you break down their equatoins.

Speed = distance / time
Velocity = displacement / time

The difference between distance and displacement is difficulat to explain but is best described as the following:

Distance is a scalar property that refers to how much ground an oject has covered during its motion.

whereas 

Displacement is a vector quantity that refers to how far our of place an object is, i.e the objects overall change in position.

The differences in these will become more apparent when studying forces and equations of motion so do not worry if you cannot get your head around the definitions at this instant