Ok, first thing is first.
Download MCSharp, and the dat to lvl converter.  These are all of the things you need to run MCSharp, however, because your on a Mac, you can't just double click the .exe file to run mcsharp and the dat to lvl converter.

This is where the Mono Frameworks kicks in.

Download the Mono Frameworks Here (I posted the link to the universal version, figured it'd be easier to put up one link for both rather than putting one link for PPC and another for Intel).
Rename the exe file to just MCSharp.exe (cause terminal won't recognize any words after a space, so do this to save yourself trouble)

Now open terminal, type

cd [path to your MCSharp server folder]
mono MCSharp.exe

As an example to show, I would type in this:

cd Users/nikalus/desktop/MCSharp-214
mono MCSharp.exe

Now, the first time you run MCSharp, the server will generate a series of files, and then the server will be up.  Each file basically acts like every other Minecraft server, but I'll do a run through of the important ones.

levels folder

this folder contains all of the files for your maps that you will have on your server.  It has all the original .lvl files of each level you make, plus a backup of those originals, and also has a folder called backups, where all of the backups are stored.  These you should delete once in a while, as you won't really ever need much more than 100 backups on each level.

ranks folder

This folder contains the following files:
advbuilders.txt
banned-ip.txt
banned.txt
bots.txt
builders.txt
operators.txt
uberOps.txt

Any username you put in those txt files will go with the corresponding rank.  ie, if I add the name nikalus to the uberOps.txt file, I will be an admin of the server.

rules.txt

Now for some reason, this file doesn't get randomly generated.  So open up textedit, write in some rules for your server, and save it as any file type.  After you save it, click the rules.txt twice (not quickly, you just want to edit the name) and replace "rtf" or whatever extention is there with "txt" (although I would suggest not saving your file as a .rtf, it'll cause some complications.)

server.properties

this is probably the most important file in the server folder.  This is where you name your server, give it an MOTD (the message that shows under the server name while it is loading), the max number of players on the server, the max number of maps that can be loaded at one time, how often a map backs itself up, etc.

Happy hosting!