If you "ställde" the book on the shelf, you put in an upright position.
If you "lade" the book on the shelf, you made it lie down on the shelf.
Standard Swedish does not have one word for "put", so you need to think of how you put something somewhere.
In northern Sweden where I come from, we have a very useful word "he", which could be used like "put", but people from the south would probably laugh at you if used that.
As a German native speaker this course is so much fun, you can see the similarities between German and Swedish in so many places :D
" Jag ställde boken.. " / " Ich stellte das Buch... " " Jag lade boken... " / " Ich legte das Buch... "
" ...på hyllan" / " ...auf das Regal " " ...i hyllan" / " ... in das Regal "
And these sentences also have the exact same meaning! If you would say:
" Ich legte die Flasche auf den Tisch " / " Jag lade flaskan på bordet "
You would at least produce a slightly confused look on the other person's face, because... Who puts a bottle on the table, horizontally?!
Ok, this was maybe a bit to much... :D
The problem is with the English preposition "in" when used with "shelf." In the discussion previously, the problem from the Swedish perspective is answered by Arnauti:
"Is there any difference between på hyllan and i hyllan?"
"Yes, på hyllan is used for things that are perceived to be 'on top' of a shelf, maybe a single shelf on the wall, i hyllan for things that are perceived to be 'inside' a shelf, maybe a bookshelf with sides and several shelves."
Later this difficulty in the difference between Swedish and English use of the words "i" in reference to "hyllan" and "in" in reference to "shelf" is discussed from an English-speaker's perspective:
"I could imagine 'into the bookcase,' since a bookcase encloses the books and usually has a front. I could not imagine 'into the bookshelf' though. Things go on shelves."