why do they take up slots in your inventory? It's weird. And the blueprint book seems useless -- and I can't google because there are too many "spoilers" associated with blueprints .... I wish there was more help in game
You put blueprints into your blueprint book so you can switch between them without having tons of blueprint objects around.Also mass import/export. (If I remember right drag-drop into the opened book to add, shift-scroll to quick-switch between the blueprints in the book?)
The blueprints you make go in your inventory by default because that's the temporary storage area for them. (Incidentally, to get rid of a blueprint in your inventory, right click it and then click on the trashcan icon in the blueprint dialog which appears).
If you want your blueprints to be more permanent and persist between games you can put them in to the "My Blueprints" section of the blueprints screen.
There you can also organize your blueprints in to books of related blueprints.
For more detailed tutorials on how to use blueprints, try searching on youtube for: factorio blueprints
It's fine to play for a bit with the new tech branches that come out occasionally in the updates.