this is my first year turkey hunting so im wondering what these are used 4 ?

It's a locater call. Turkeys will gobble to it.

just curious why ? and is it a good idea to buy one?

Its just another tool in the bag. Its used to shock a bird into gobbling. Once you know where he is, you put it up and get in range of him and start hen-talking to him.

Yes its a locator call to shock the tom into gobbling. It can be quiet and when you use the call he may gobble and it also will get crows to start cawing and he will keep gobbling at them. Sometimes you have to watch what the crows do as well. Sometimes they will swoop down at the turkeys. If you pay close enough attention to them they can also give a turkeys location away.