I found the use of a dibber helped push the paper down. With the paper in place its easy to fill them with soil. Once filled with soil you can then put whatever seeds you like in.
This method of sowing seeds would work particularly well with plants that don't like bare root planting like runner beans and beetroot. I have sown sunflowers, which bring in lots of valuable insects to the vegetable patch. I will keep some seeds for next year and the rest can be saved for the birds to eat over the winter. Not forgetting they are also such a lovely cheery flower to have growing in your garden.