It makes sense to have a guide on how the librarian should use the administrative bits on here, or more specifically - how to deal with people wanting books out of the library.
Firstly, it's probably best if you read about getting a book out of the library as that's where everyone has to start. It's also worth making sure you're logged in too, as there are lots of extra features within the library that only appear then.
The way the whole taking books out things work is done over a series of stages
You can see what stage a book is in on the book history page. This page also lets you progress a book's state to the next stage. To save time and because it's likely that you won't have access to the website whilst rummaging around in the books, you can implicitly do steps 2 or 4 by selecting steps 3 or 5 respectively. It's also possible to transfer a book between members if someone requests a book that someone else also has.
When taking books out of the library, it'll list what editions are available so if there are multiple editions, it's a good idea to make sure you mark the right copy as having been taken out. It also lists the location in brackets in the form (cupboard.shelf.row.column). Shelves are numbered 1 to 7 from the top. Rows are numbered 1 to 3 from the back of the shelf. The column is 1 to X from left to right.
Putting the book back where you got it from is a good idea, but if you don't, then updating the location will ensure that subsequent librarians can find the book quickly and easily.