First install mercurial in your system if you haven't done so.
You can get it from here or from your distro package manager.
Then do the minimal configuration, as explained here.
To clone the repository(anonymously):
hg clone http://hg.code.sf.net/p/kissplayer/code kissplayer-code
To clone the reposutory(with R/W access):
hg clone ssh://[username]@hg.code.sf.net/p/kissplayer/code kissplayer-code
Then you can start playing with the code. Once you finish working on a bug or a new feature, you should generate a patch for submission.
I strongly recommend using Queues, checkout this nice article by Mozilla.
But if you want something fast and simple, try the following:
Make sure the local repo is synchronized and clean:
hg in
hg pull
(If there are commits pending)
hg st
(Check the repository state)
Now create the patch(do not commit):
hg diff -g > ~/patch.diff
To revert all uncommited changes(with no backups):
hg revert -C -a
If you want to learn more about Mercurial, this tutorial by Joel Spolsky is a must.