Older, 240-volt electric dryer receptacles have three prongs, attaching to three wires -- two hot leads and one neutral. New codes require a four-prong receptacle, which connects to two hot wires, a neutral, and a ground wire.
If a dryer cord does not match the receptacle, hire a pro to change the receptacle or change the cord yourself. The following steps show how to change from a three-wire to a four-wire cord. (Do not change from a four-wire to a three-wire. You will eliminate the ground wire, which offers extra protection against shock.)
About 1 hour to remove the old cord and install a new one
Screwdriver, drill, and perhaps strippers
Drilling a hole into metal; attaching wires to terminals
A new dryer cord and a grounding screw with a head large enough to capture the cord's ground wire