Breaking down an application by release version is usually done in tags. So you would have a /tags/ directory inside of which you would have 1.0/ then 1.5/ then 2.0/ etc. You could of course tag pre-1.0 versions as well...

Branches are used when you want to make changes without modifying the trunk, usually if you have some reason you want to start a separate project. Sometimes a branch is created if you just have a lot of work you want to do in a big block with a plan to merge those changes back into the trunk later -- this allows people to continue working on the trunk separately while you can commit many changes to the branch without interfering with them or slowing them down.

Generally speaking branching should be kept to a minimum. With tags by comparison, more may be better.

Welcome. :)