This is an eBook on SVN. It is long and incredibly thorough, so I don't expect anyone to read the whole thing (if you did, you'd probably know more about it than I do ). But you can browse through it to figure out the basics at least. Flip through chapters 1,2, and 4.
That describes basic concepts, but it doesn't really go into the trunk-tag-branch structure. Basically in the SVN repository itself, at the top level, you have a trunk folder, a tag folder, and a branch folder. The trunk folder is the current state-of-the-art source code as people are working on it. Tags represent a forks at a specific moment in time. For instance, everytime the program is released with a new version number, you'd want to create a new tag. Branches are experimental forks with changes that may or may not end up integrated into trunk at some point. There a way to experiment without breaking anyone else's use of the code.
So the top level of the repository should look like:
Trunk
Tags
Branches
So what I want you to do basically is create tags and branches folders. There's a command in Smart SVN to do this (look under tag/branches in the menu). Then create a branch into the tags folder labeled "2.43" (or whatever version is in there right now if you can figure it out). Then go back to trunk.
The download the latest source from the FTP, and copy that into your working copy. Then commit that to the trunk. Then take the new trunk and tag it as 2.44.1 (or whatever is the latest version). Then go back to trunk. Decide if
all of your personal changes should committed to trunk. If not, you can create a branch called Botsareus in the current Branches folder. Then copy your personal changes to your working copy, and then commit it to the repository. From there you can attempt a "merge" back into the trunk and decide what changes you made should go into trunk, and which should stay as part of your personal working copy.
I can probably figure out a temporary SVN repository if you want to practice this stuff.