The book's call number is like its address on the shelf.
BS500 .Y37 2004
To find it, go one line at a time. First, you need to look for the letters (in alphabetical order), then the numbers. On the shelf it will be vertical.
BS
500
.Y37
2004
The first number is a whole number (and sometimes a decimal too).
The second number is always a decimal.
These books are located on the 3rd floor.
Reference books will have a REF preceding the call number
REF BS500 .Y37 2004
Reference books are on the first floor.