I know this is pretty easy to find with a google search, but still nice to write it down.
On mac you want to install git svn:
"sudo port install git-core +svn"
Next you create an authors file (authors.txt) to convert the svn contributors and keep the full history:
buck = Buck Mulligan <firstname.lastname@example.org> hans = Hans Castrop <email@example.com>
The simplest command if only want to convert your trunk:
git svn clone --no-metadata -A authors.txt https://svn.example.com/code/trunk
To convert branches/tags see: http://pauldowman.com/2008/07/26/how-to- convert-from-subversion-to-git/