I made a book in Illustrator, and I would like to replace a word with another word (e.g "Bread" into "Rice"). If I was using MS Word, I could simply Ctrl+H and do a word replace. How about in Adobe Illustrator?
Go to "Main menu > Edit > Find and replace".
It's exactly the same as other applications, just without the keyboard shortcut (it's a less commonly used feature, and those keys are used for other things: CTRL+F for Paste in Front, CTRL+H for Show/Hide Edges).
Incidentally, making a book in Illustrator is quite unusual. It's more common to assemble the book in InDesign and use Illustrator for illustrations, which are then placed into the InDesign file.