Make sure that Warcraft Demo and War Demo Data are in the same folder. That's it. If your demo came with a War Demo Movies folder (demos distributed on CD-ROM do), then make sure that is in the same folder with the other two files. You can make aliases to the War Demo Movies folder and the War Demo Data file if desired, and you can also run the entire program off CD-ROM if necessary.
There is help under the Apple Help menu (the one on the right with the Question mark). Other than that, game buttons describe themselves when the mouse moves over them.
Select a unit or units, then click the button for the action to carry out, and then a target (some actions do not have targets). Crush the enemy. Have fun.
To play a two-player game, you will need to have some Communications Toolbox tools. The AppleTalk ADSP tool is used for network games, the Apple Modem Tool is used for modem games, and the Serial Tool is used for direct-serial games. If you have MacIPX, then you can use IPX for network games as well.
The full version of Warcraft ships with relevant Comm Toolbox tools and MacIPX, to allow Mac-to-Mac and Mac-to-IBM games of Warcraft.