I don't remember what the little metal plates are called, but at Lowe's they were hanging right next to the table legs. The legs have a threaded metal piece in the top end. The hardware that is sold
separately has a threaded hole for the leg to fit into and 4 holes to screw it into the under side of the table. Just be careful to buy the right type. One kind will hold the table leg perpendicular to the table (that's what you need) and the other kind will cause the table leg to be at an angle to it. I'll attach a pic of one of them.