Putting together and external HD. so I just purchased and internal drive to go into my existing

Question

so I just purchased and internal drive to go into my existing externalcase but I think i ordered the wrong drive because the connectors fromthe external case are the wrong ones for the internal.. Need somehelp.. heres what i ordered from newegg http://www.newegg.com/Product/Product.aspx?Item=N82E16822136113&Tpk=22-136-113 obviously im new at doing this but a friend suggested that its the way to get go with buying externals