This is the process of joining the book block or pages to the hard cover. This can be a bit tricky but gets easier the more you practise.
You will need:
PVA glue and brush, scrap paper, pressing board and weight.
Glue Tips: You can mix a little home-made wheatflour paste to the PVA to make it slightly wetter. This gives you a longer drying time when sticking down the endpapers and can even give you time to reposition the pages if you don't like where they have ended up inside the cover! If you have used a bit too much glue and it is squeezing out from under the endpapers, use a sheet of non-stick paper inside the book when you press it. This could be the backing of sticky label paper, wax paper from inside a cereal packet or greaseproof baking paper.