First you need to find a scroll of identification:
1) Sin city
2) New Barter Ground
3) Farm locations
Buying scrolls of identify 1
Buying scrolls of identify 2
After that:
1) insert the scroll in the slot for scrolls
2) put thing in slot 2
3) click on the (book)
4) in the window that appears, click on the Identify!
And all thing identified!