Just to get in the mood for it, first you have to read that lengthy
introduction to git-svn for Subversion/SVK users and deserters. You're so not expected to read that page through to its end at the first attempt, so instead you're expected to refer to it again sometimes after your first hand-on experience. Here goes:
cd my_unversioned_project
git init .
git add .
git commit -m "initial import"
# hack, hack
git add modified_file_1 modified_file_2 added_file
# (at this stage, be sure to know what the "index" is)
git commit
and work that way locally for a while, venturing into branching (remember: git is about having plenty of small, not so short-lived, feature branches) and then merging until all that you see in the gitk --all and git ui GUIs make sense to you. Or, why not, cloning your repo/directory, and pushing from the clone to its "master".
Overall at this stage, the github usage docs and getting started are your friend. After this learning phase, stackoverflow will come in handy :)
Last, don't be too afraid to try things on working copy with clean status, since git commands only affects the .git repository in an append-only fashion, you'll be able to revert on every command that turned awful:
git reset --hard HEAD@{1}
will take you to the previously recorded state of your repository. Just look into git reflog for past things not necessarily in "gitk --all".
Short, only one links, but hope this will help.
Hal.