Short

Want to set automatic (or at least semi-auto) software version numbering in GIT

Detailed

I'm newby to GIT. Recently created some bare git repo and made some commits and pushes into it. Want to set some starting version number (like v1.0) to my project. I know, there is tag for this reason. Googled it and found bunch of materials. For example:

git - the simple guide blog says:

You can create a new tag named 1.0.0 by executing git tag 1.0.0 1b2e1d63ff the 1b2e1d63ff stands for the first 10 characters of the commit id you want to reference with your tag.

Kudelabs says:

$ git tag -a 'milestone1' -m 'starting work for milestone 1, due in 2 weeks'
$ git push --tags

I'm really confused. What is difference between first and second method: git tag and git tag-a. Can't figure out which to use for this purpose.

How can I set version number in bare remote repo, to which I made 5-6 commits and pushes?