Control-click on the file that is unarchived after clicking the .zip file, and then a menu will appear, as is whenever you control-click a file. Click "show package contents". There're the programs you're gonna use. Double-click any of them to use. Here's a summary:
-allows you to convert .bar files into folders, after specifying the location in which you would like them to be placed.
-allows you to convert .xmb to .xml and vice-versa, and .bar to .tga and vice-versa. In order to edit .tga, just use GIMP or any other software that edits photos for mac. Then you can change the texture (or "skin") of units- (*but not the shape, since you need some $12,000 software for that), and also the flags of civilizations, etc.
-application that allows you to run windows applications on mac, and also creates a C-drive directory. Works virtually every time for me.