In order to master a program you have to begin at the basics- the terms or names that the program gives to each part of its interface. Fortunately there are only 4 things that you need to remember:
1. Top Menu
From here you access all the necessities like creating/opening an image and closing it, or cut, copy, pasting, or adjusting the view, manage the image and layers, apply effects, switch between windows or getting help.
2. Dock (Left)
The left side dock for placing tabs. Notice that the toolbox tab can't be interfered with, it always remains at the top and can't be moved vertically. The rest, however, can be moved around and resizes just fine.
The main working area. You'll probably have your eyes here 80% of the time. This is where you see your image and edit it.
4. Dock (Right)
The right side dock for placing tabs. You can stack tabs on top of each other or have them above/below to save space yet keep them open.
At the very bottom is the status bar that offers some info based on what you're doing. If you're creating a selection it'll tell you the size and aspect ratio of it for example, or if in the top menu it'll give you a short description of what the menu function does.