Geometer works on Windows 95/98/NT and Linux machines. It also works on Macintosh machines running OS/X. This is documentation for the 95/98/NT version, but it is almost completely correct for the versions of Geometer that run on the other platforms.
Load the CD into your drive and run the install script. By default, Geometer will install into the directory C:/Geometer but you can put it elsewhere. All the interesting files are in that installation directory which contains a file called README that describes the arrangement of the installed files.
All Geometer diagrams are files whose name ends in .T or .D (the .T files are generally more interesting---they are theorems, and the .D files are simply drawings used in documents). You can view any of them by double-clicking on the diagram's icon.
Geometer diagrams consist of points, lines, circles, and so on. The only thing you can manipulate in the drawing area with a mouse are some of the vertices. (If it's necessary to have a movable line in a diagram, that line is usually a line going through two points, and you can move one or both of the points to move the line. Similarly for all other non-point objects.)
To move a point, use the mouse to move the cursor over a point. Press down on the left mouse button, and move the mouse with that button held down. If that point is movable, the diagram will shift appropriately.
If the diagram is a proof or construction, you will almost always see in the "Layer Control" section of the control panel on the right side of the screen that only layer number 0 is checked---numbers 1 through 15 are background gray. If the diagram is like this, you can click on the "Next" button to the right of the 16 indicator lights to advance to the next step of the proof/construction. You can begin again by pressing "Start" or you can go back one step by pressing "Prev" (for "previous"). Do not click on the 16 layer indicator buttons or you'll probably get strange results. (And if you do, you can always press "Start" to begin again.)
Even if the diagram is a proof or construction, you can still manipulate the points as you step through. For example, suppose you get to a step in the proof that says, "Therefore, points A, B, C, and D all lie on a circle." If you don't believe it, you can at this point modify the drawing by moving points to see that in fact the four points do continue to lie on a circle. Then once you've convinced yourself, you can continue with the proof or construction.
Finally, some diagrams have scripts. If the "Run Script" button in the control panel is not grayed-out, you can press it to run a prepackaged script. You can stop the running by clicking in the drawing window, or by letting the script run to completion.
In most cases for the prepared diagrams discussed above, each screen will contain instructions for how to proceed, like "Press 'Next' to continue ...", or "Press the 'Run Script' button." Diagrams that are just used for drawings (generally having a .D suffix) or that were obtained from other sources may or may not have good instructions, so in those cases, you're on your own.