Cut your chosen material to two Cm's thicker than needed on three sides of the book cover
Now Iron half a cm in on each of the three sides
Glue the neat side onto the front of the cover. You only need one line of glue on the left hand side. Use strong glue.
Turn over the cover page and glue in each of the three sides pulling tightly
And then glue on a sheet of thick card or paper. Done. Easy