Subversion (Svn) has an easy tree structure concept for project versioning.
It has a main trunk, a tag and a branch, each on its own location:
This is the common structure.
The trunk is were the daily development goes. Here’s a couple of examples:
The tags is where a tag goes. Here’s the same example:
The branches is where where a branch goes. Again, the same example:
For more information about Svn, read Version Control with Subversion.