Whether it is keeping your creative pieces for future reference, as a storage solution, to share with others or as a gift, making books is a very calming and grounding experience. Old books can also be repurposed (see altered books below).
An easy to follow guide to making books from scratch can be found here: https://www.instructables.com/id/DIY-BookbindingBookmaking/
Repurposing published books initially went against the grain for me, but over time I have used this activity often in a therapeutic space, and it has become a real favourite.
There are many websites and images about altered books but for me the key things are:
Choose a book that "speaks" to you.
Choose a book that you are comfortable to "repurpose"...probably not a signed first edition of Wuthering Heights, or a religious book or family treasure.
Charity shops are amazing for sourcing books.
I try to choose a book with a strong spine, ideally a sewn one and a good strong cover (although you could make a cover).
I might stick pages together for a stronger canvas, or paint with a primer like gesso. (Available from Warehouse Stationary)
Take something from the page...that jumps out at you, and work with that.