I have a repository named "Celerado" which includes various projects setup through GIT.Now as I have just migrated from SVN to GIT, How can I create authentication on Git?How to add users to Git?

Git doesn't have a separate authentication system, it relies on file permissions. To give people write access to a repository on a server, give them SSH access and write access to the files. You can use git shell with this. The git daemon service is for providing read-only access.

Few Doubts more..Say, I have 10 users who wants to access GIT Repository and work with the same.
I just migrated my SVN to GIT and while migrating the tutorial taught me creating a file called svn-to-git file as:

As out of those 5 members will be working on a project called ITES, I need mail to be sent to those only 5 members and not to all others associated.
Someone suggested me Hook script but no idea how it gonna happen. Can you help me with this?

Every time that Git carries out an action, it looks in the .git/hooks/ directory for a file with a particular name, and runs it. The file could actually be a symlink that points to a file somewhere else on the system.

The man page for githooks explains:

http://www.kernel.org/pub/software/s.../githooks.html

You can use any scripting language, such as Perl or Ruby, not just shell, and I don't think that the script has to follow any special format, so you can write whatever code is best or easiest to get the list of addresses and send emails. Some examples are quite long, but there's nothing wrong with writing something very simple.

There is a large example post-commit hook script to send emails (written in shell) provided with the Git documentation, in the file /usr/share/doc/git-core/contrib/hooks/post-receive-email - it gets a list of addresses stored in the repository settings file, using the git config utility.