Once I went back to an older version - alas, all the later versions were lost. After reading some books in git, I realised that I should have branched from an older version. Thus if you are planning to experiment, it is better to branch to a new branch and experiment. If the experiment is successful, you can merge back into main stream. So easy!
The branch command is:
git branch branch_name tag_name(or commit hash)
to checkout the branch
git checkout branch_name
It is extremely comfortable to checkout branch and then merge into...
git mergefor merging and for visualization of log, one can use
git log --graph --pretty=oneline --abbrev-commit
Now the eclipse git plugin provides branche/merge etc...making life more comfortable!
Thank you Linus Torvalds