Bonsai is a way of pruning and restricting the growth of a plant so it stays very, very small. The shape the plant grows is also changed, often making the plant look like a tiny, old, twisted tree.
Bonsai is achieved with a combination of careful pruning of both the roots and the branches, and using wire to shape the branches as they grow. Keeping the bonsai in a small container keeps the plant small, but great care must be taken so the plant doesn't dry out and die.
A book is made of many sheets of paper or parchment, bound together down one side. Each sheet is called a leaf, and each side of a leaf is called a page. Books can have lots of pictures or just words. They might have a story in them that is all true (non-fiction) or a story that someone has made up (fiction). Reading books is a hobby a lot of people enjoy.
A bookshelf is a piece of furniture that is used to store books on. Bookshelves can also be used to store anything that fits on them, but most people do use bookshelves just to store books.