EDIT: MacMiner now includes the QuarkCoin CPU miner - check it out if you'd rather use an app for mining

First, you need to download (or compile yourself) the cpu miner app:

http://downloads.fabulouspanda.co.uk/minerd-quark-mac.zip

The above link is the compiled code (minerd) from this Github: https://github.com/rallat/quarkcoin-cpuminer As well as the dependencies it requires, curl and jansson

Unzip minerd-quark-mac, then open the 'Terminal' application in the Utilities folder to run at the command line.

Drag the minerd-quark-mac folder when decompressed in to the Terminal window after typing cd then press return, e.g.:

cd /Users/name/Downloads/minerd-quark

then type the following in Terminal, replacing the pool and user information with your own:

./minerd -a quark -o stratum+tcp://www.mine-pool.net:3350 -u username -p password

If you have any problems, leave a comment or get involved at the Mac mining forums: http://fabulouspanda.com/forum/