How is a tag different from a branch in Git? Which should I use, here?

I am having some difficulty understanding how to use tags versus branches in git.

I just moved the current version of our code from cvs to git, and now I’m going to be working on a subset of that code for a particular feature. A few other developers will be working on this as well, but not all developers in our group are going to care about this feature. Should I be creating a branch or a tag? In what situations should I be using one versus the other?

A tag represents a version of a particular branch at a moment in time. A branch represents a separate thread of development that may run concurrently with other development efforts on the same code base. Changes to a branch may eventually be merged back into another branch to unify them.

Usually you’ll tag a particular version so that you can recreate it, e.g., this is the version we shipped to XYZ Corp. A branch is more of a strategy to provide on-going updates on a particular version of the code while continuing to do development on it. You’ll make a branch of the delivered version, continue development on the main line, but make bug fixes to the branch that represents the delivered version. Eventually, you’ll merge these bug fixes back into the main line. Often you’ll use both branching and tagging together. You’ll have various tags that may apply both to the main line and its branches marking particular versions (those delivered to customers, for instance) along each branch that you may want to recreate — for delivery, bug diagnosis, etc.

It’s actually more complicated than this — or as complicated as you want to make it — but these examples should give you an idea of the differences.