The four-sided dice (also known as a d4) is one of the most distinctive dice out there. Obviously its shape really makes it stand out: The d4 is traditionally a tetrahedron, or pyramid shape, so there is no topmost face to easily indicate the result of a roll. This means that the results on a die may be displayed differently depending on the dice manufacturer. On some 4-sided dice, the result is indicated by the number that is shown upright on all three visible faces. This number might be near the apex of the die or it might be located along one of the sides. On other d4's, three numbers are shown on each face and the result of a roll is the number that is displayed along the base, on the downward side.
Four-sided dice are known for not tumbling very well when rolled. When you toss them they tend to plop onto the table and stay there. So the best way to roll a d4 is to give it a good shake prior to throwing it, and then give it a slight spin when you let it go from your hand. Either that or you could use a dice tower to ensure that the dice tumbles sufficiently.
A note of caution: Don't leave your d4's lying around on the floor. They tend to be quite painful when stepped on. Not as bad as stepping on a Lego, but it's still an experience to avoid!