Cut them into 28-32" lengths. I think 36" would make them quite heavy. Then lay them flat next to each other in a horizontal row of 6-8 (4 feet total) Whatever is manageable to move around (once floating). Then 3 or 3 'stringers' down the length to tie them together. It is fine if it is flexible stringer like chain, or cable or even thick non-rotting rope.

These then need a lead rope on them and you lay them out in the pond. For a few months they will float on their own till they get waterlogged. These become the flat 'mats' that the fathead minnows will attach their eggs to on the underside. Eventually they will waterlog and sink. So planning ahead you can either add old foam board or other plastic floats on the underside to keep them suspended near the top, or you can put props of some type under the 'mats' so that when it waterlogs it stays at least 24" or so off the ground.

There are pictures in the archives somewhere of larger mats that a member made, maybe 10-12 feet long total but they get unwieldy to move around if they are too long.