The drogue is used to help slow your drift speed in certain conditions i.e: wind over tide. There are many sizes and shapes but all do the same job, most are made from a rip-stop material. Generally, you tie rope 6ft or more to a clip & connect to anchor trolley.
It is connected to your anchor trolley then positioned forward, rear or to the side dependent on the conditions on the day. A very useful method when lure fishing.