Installing Therion on a Mac is like caving without lights. You will not get very far before you get lost, confused, and hurt yourself.
In addition to Compass you will need a vector graphics drawing program. Use Inkscape. It is supported open source (free) and has versions that run on both Mac and Windows. The Compass tutorials for Inkscape are very good. The tutorials for Compass are in general very good.
I am a Mac fan but rather than run Compass on a Mac you can buy a cheap laptop, like a netbook, and load it up with memory (RAM) or go by a pawn shop and pick up a cheap desktop (spray it for bugs before you bring it into your vehicle or house). Extra memory is cheap and widely available. It comes in really handy when you are using the Compass feature to join sketch segments together.
Finally you will need a drawing tablet so you can draw with a pen rather than clicking and dragging with a mouse. I just looked on EBay and found an acceptable used one in seconds: a Wacom CTE-430 (Sapphire) for $25. The bigger the better.
Mike Rogers recently took up survey with Compass and Inkscape and quickly turned out a really nice map. Search the Tag-Net archives for more information.