I was supposed to attach it to the seat post with a provided clip but I like to live dangerously so I attached it to the frame with zip-ties instead. The duct tape is there to prevent the frame from getting scratched and the grip tape keeps it aligned and from moving around.
I had to improv with mine, too. They’re chrome fenders for an old man cruiser, but they aren’t made for bikes with caliper brakes. I put them on, then couldn’t stop. So, I had to pound some indentations in for the calipers. Problem solved.