Options Bar and Menu Bar
The Options Bar at the top of the screen gives useful feedback on each tool as it is selected. It will change in appearance according to what tool you have selected. This bar is twinned with a Menu Bar that presents various Screen Mode commands (full screen, magnification etc).
Tip: You will often need to spend a little bit of time fiddling with the tool settings in the Options Bar before you can use it. fifty percent of the time that something is going wrong in PS it is because the settings are not as they should be.