The key difference is that git is decentralized. Imagine you are a developer on the road, you develop on your laptop and you want to have source control so that you can go back 3 hours.
With Subversion, you have a Problem: The SVN Repository may be in a location you can't reach (in your company, and you don't have internet at the moment), you cannot commit. If you want to make a copy of your code, you have to literally copy/paste it.
With Git, you do not have this problem. Your local copy is a repository, and you can commit to it and get all benefits of source control. When you regain connectivity to the main repository, you can commit against it.
SVN has the advantage that it's MUCH simpler to learn: There is your repository, all changes to towards it, if you know how to create, commit and checkout and you're ready to go and can pickup stuff like branching, update etc. later on.
Git has the advantage that it's MUCH better suited if some developers are not always connected to the master repository. Also, it's much faster than SVN.