in order to teach the "drop" command, you will need two items in order to "trade off" one item for the other. the two items should be toys that they are particularly fond of.
give the first toy to your dog and allow them to play with it and get it in their mouth.
now this is very important, keeping the second item out of their sight until you are ready to present it to them, place it directly in front of their muzzle so they can see and smell the item while simultaneously saying the command "drop"
the object is to get your dog to open their mouth, releasing or "dropping" the first item, in trade for the second item. immediately praise your dog once they perform the act of "dropping" the first item. timing is important so your dog associates the "drop" command with the proper action.
as soon as your dog is focused on the second item, take the first item back and hide it from them, placing it behind your back. once they continue playing with the second item, bring out the first item and repeat the exercise all over again. shouldn't take long for your dog to catch on.
treats can eventually be incorporated during praise in order to strengthen your dogs response to the command.
hope that helps.