On OSX, you can use SVN either using contextual menus with svnX, either using the command line.
When using SVN for the first time, you have to use the command line.
Please, follow the instructions

Download and install Subversion SCPlugin

Download and install the stable SCPlugin installer.

Using the command line first

Open your terminal:
/Applications/Utilities/Terminal.app

Set path preferences using nano:
Open .bash_profile nano .bash_profile

then type: alias svn='/usr/local/bin/svn'

then quit nano by pressing ctrl-x
Move to the directory where you want to put Jamoma:
cd ~/Documents

Run svn:
svn checkout https://jamoma.svn.sourceforge.net/svnroot/jamoma/branches/active Jamoma For more information about svn and Jamoma, check the documentation for using SVN with Terminal.

Using contextual menus with svnX

Download and install svnX

1. Download and install svnX
2. 
   

Using SCPlugin?

1. Download and install SCPlugin
2. Log out and back to have it active.
   
3. Create a folder where you want to install Jamoma
4. Right click (or ctrl-click) on the folder to get the contextual menu
5. Choose checkout and enter one of the following adresses, depending on which version of Jamoma you want to use and work on :
   
   - For users looking for the most recent stable version, you want to check out from the trunk : https://jamoma.svn.sourceforge.net/svnroot/jamoma/trunk/Jamoma
   - If you instead want to use and work on development (at times this will be less stable), you should checkout the active branch : https://jamoma.svn.sourceforge.net/svnroot/jamoma/branches/active
6. Or Use the subversion commands available at the bottom of the menu

Then unzip everything in the Jamoma/library/externals and move the Jamoma framework to Your_Drive://Library/Frameworks.
(you can also read the ReadMe?....)