title: Revert many commit after the creation of a branch
body: <p>i'm using git to manage my project, but i'm not much experienced in this kind of programs, so often i use them improperly(eg: i commit many (unrelated) changes in only one commit). I'm trying to using them better.</p>
  
  <p>Btw i noticed that i started to develop an extension of my project that would be better fitting into a branch. So from the git gui i created a new branch that's a copy of the master.
  Now i want to revert the master to the last commit i made that it is not relevant to the project. I know what this commit is, but i don't know how to revert all the commits from HEAD to this one, and i don't know if this will influence the branch(it would be a real pain to lose all the new work..)</p>
  
  <p>So, how can i do?</p>
  
  <p>Ps: usually i use git gui, but i have no problem in using git bash. I use win7 and i'm managing an java android project in eclipse</p>