Here is a screenshot illustrating single-window mode, which I strongly recommend you use.
The image panel in the center is flanked by left and right panels which are fixed; you can't move them. But you can decrease or increase their width. If you reduce the width of a multi-tab dock, there may be not enough place for all tabs; then arrow-heads appear allowing you to scroll through tabs.
You can mask the left and right panels using the Tab key.
When several images are open, a new bar appears above the image panel, with a tab for every image. You can navigate between images by clicking on tabs or either using Ctrl+PageUp or PageDown or Alt+Number. “Number” is tab number; you must use the number keys of the upper line of your keyboard, not that of keypad (Alt-shift necessary for some national keyboards).
1 The Main Toolbox: This is the heart of the Gimp. It contains the highest level menu, plus a set of icon buttons that can be used to select tools, and more. For help with the various tools press F1 while in the GIMP and check out section 3 of the GIMP help system.
2 Tool options: Docked below the main Toolbox is a Tool Options dialog, showing options for the currently selected tool (in this case, the Free Select tool). Several other 'dialogs' are also docked in this window and you can switch between dialogs by clicking the corresponding tab. For example, to switch to the brushes dialog, click the second tab. In addition to the Tool Options and Brushes dialogs, I recommend that your basic layout should include the undo history dialog and the layers dialog.
3 An image window: Each image open in Gimp is displayed in a separate window. Many images can be open at the same time: the limit is set only by the amount of system resources.
4 The Layers, Channels, Paths, Undo History dock — note that the dialogs in the dock are tabs. The Layers tab is open : it shows the layer structure of the currently active image, and allows it to be manipulated in a variety of ways. It is possible to do a few very basic things without using the Layers dialog, but even moderately sophisticated GIMP users find it indispensable to have the Layers dialog available at all times.
5 Brushes/Patterns/Gradients: The docked dialog below the layer dialog shows the dialogs (tabs) for managing brushes, patterns and gradients.
The easiest way to get help in the GIMP is just to point at the item in question - a brief description will pop up. The GIMP also has a fairly good help system - you can get help at any time by pressing the F1 key or from the Help menu. This will open the user manual. The user manual has an index but is not searchable. Alternatively you can get context-sensitive help by choosing Help>Context Help or by pressing Shift-F1. The pointer will change into a question mark and you can then click on the item (tool, tool option etc.) that you want help with (I don't think you can get context sensitive help on menu items, however).
Brilliant student though you may be, it's just possible that you may make a mistake or two during the course of these lessons. Luckily for you, the GIMP has powerful 'undo' features. Edit > Undo or Ctrl-Z will undo the LAST change that you have made but you can undo many more steps by using the Undo History dialog (the number of steps is set with Edit>Preferences>Environment>Maximum number of undo levels. This is 5 by default - don't set it much higher than that unless your computer has a huge amount of RAM.
If you want to to revert to the image as it was when it was last saved then choose Revert in the File menu.
Acquiring, opening and viewing the images
If you are lucky enough to be in my class I will tell you the location on the network of a folder containing all the images you will need for this class - simply copy them (e.g. with Windows Explorer) to your own folder. If you are not in my class then for each lesson you will need to right-click the image on this website and choose 'save target as...', saving the copy of the image onto your computer. Then you can open the image in the GIMP by choosing File>Open. Make sure that the Dot for Dot option is turned on in the View menu - if this is not turned on then the Zoom numbers become almost meaningless, so leave it on all the time.
Another way to get an image into the GIMP from a web page would be to copy the image and then, in the GIMP, choose File>Create from Clipboard. In this case you will need to be especially careful when you save (export, see below!) the file since you will need to give it a meaningful name.
Once you have got the image into the GIMP I suggest that you choose View>Zoom>Fit image in Window (or Shift+Ctrl+ J) to make the image as big as conveniently possible.
To zoom in and out use the + and - keys or choose the Magnify Tool and click to zoom in or Ctrl-click to zoom out. Or just hold down the Ctrl key and roll the mouse wheel. Or use the zoom adjustment at the bottom of the GIMP window. If you can't see the whole image in the window (because you have zoomed in) then you can move around the image using the navigation control in the bottom-right corner of the image window.
If you want make the image zoom automatically when you resize the window then make sure that the 'zoom image when window size changes' button in the top-right corner of the image window is turned on ('pushed down'). Note however if that option is turned on then Shrink Wrap (Ctrl-E) won't work properly.
I suggest that you keep keep your screen as simple as possible by keeping the Rulers turned off(View>Show Rulers) all the time unless you really need them.
Saving your work
You should be able to produce some beautiful, high-quality work in this class and you won't want to lose it, so save your work at least every 10 minutes. In this way, even if your computer crashes, you can be sure you will never lose more than 10 minutes' work...
Work-in-progress is best saved in the GIMP 'XCF' format which will save with no loss of image quality and record all the details about the image, including information about layers. However, XCF files are very large and therefore once the image is finished you should save it (export it) in a compressed format such as JPEG. When saving (exporting) in this format increasing the compression comes at the cost of decreasing picture quality - you can control the balance between small file size and high picture quality - a setting of 90 (out of 100) is recommended for this class. Use meaningful names when you save - it will make it easier for me to locate and grade your work.
Remember that the Save command does not work the same in the GIMP as in other programs. In other programs if you open a file in a certain format (jpeg, for example), modify it and 'save' it then it will be saved in the original format, overwriting the previous file. In the GIMP the 'save' operation ALWAYS saves in the GIMP's native format, XCF. If you want to 'save' in the original format you have to choose 'Export To' in the File menu (Ctrl+E). Similarly, 'Save As' does not work as expected - it ALWAYS saves in the XCF format. The equivalent to the 'Save As' command of other programs is File>Export (Shift+Ctrl+E).
In my online lessons you should assume that when you are told to 'save' your work you should choose 'Export To' and not 'Save' in the File menu.
Understanding Digital Images
Click HERE for an introduction to color, resolution and image formats, all of which are important concepts when working with digital images.