Applications should be usable without training or external documentation, including the "Using this database" document.
Any instructions that might be needed should be included on the screen next to the place where they are needed. I typically make the instructions small (size 8) and red to differentiate them from the active form.
Longer instructions can be placed in a pop-up window. The trigger should be obvious and really close to what the instructions affect.
Extra instructions can be placed on the right side of the screen if the data is short.