Android isn't complicated, but being bale to use custom launchers require some knowledge of the nomenclature.
App Tray or App Drawer contains all application installed on your device.
Widgets are little apps that run and provide status information. Up until recently they could not go on your lock screen but now they can, though the widget write has to explicitly support it.
The Launcher is the part of your Android device that gives you your "Home screen". This is where you have your shortcuts to the apps you have installed, and your widgets.
Home Row is the bar at the bottom of your home screen where you have your favourite apps.