To use them a loop on the long end is pushed through your boot laces near the hem of your trousers and then the knot pushed through the loop to temporarily secure them.
The cord and then the fabric band is then wrapped around the bottom of your trousers until you come to the cord on the other end which is then just pushed under the last wrap of the cloth band.
Because there is a knot at the end of the short cord, that tends not to slip out from under the band which secures things very well. The other end being fastened to you boots also stops the trouser hem from riding up.
The intention is to prevent snow from migrating up under your trouser leg and into the top of your boots and this they achieve perfectly.
When removed they are simple and quick to dry out too. Much less fuss than gaiters.