Think of SVN like a tree. The trunk is the main part of the repository where our current working version of the code goes. The branches are deviations separated from this trunk that were used to make some modification (without disturbing the trunk). The tags just mark a certain version in the repository.
If you want to get the code for VDrift from SVN you want the trunk. You can check it out like this:
Code:
svn co http://svn.vdrift.net/repos/vdrift/trunk vdrift
This will make a new directory in the current one called vdrift, and it will check out the latest code from the trunk and put it there.
