You can search directly from the search box on the front of the Library website.
What is a classmark? As you walk round a Library you will notice that books on the same subject are all in roughly the same area of the Library. This is because every book carries a label on the spine indicating where on the shelves it will be filed. The label usually contains a three-figure number followed by a decimal point, with numbers and letters following this decimal point. These numbers aren't random - they correspond with specific subjects. The Library uses a list of numbers to create a classmark.
When you find the item via Library Search, availability is shown, as is the location and the loan period.