By default you will enter the staff client as if you are at your home library. This library will appear in the top right of the Staff Client.
This is the library that all circulation transactions will take place at. If you are at another library (or on a bookmobile) you will want to set your library before you start circulating items. To do this you can click 'Set' at the top right or on the Circulation page.
Once you have saved your changes you new library will appear in the top right.