newbie question - git-pull and local branch merge

Hi,

I'm quiet new to git and I have done this so far:

1. Installed git-1.4.4
2. pulled linus kernel tree.
3. Created a local branch 'git-checkout my stuff'
4. Edit a number of files.
5. git-commit -a
6. git-pull
7. Edit a couple more files.
8. git-pull <- Problem!

Accidentally I had 2 files not committed and one of these also
had changes in the git-pull master branch which git could
not merge automatically.

Changes has been done but I'm not fully convinced what has happen.
I see that files has been changed and the failing merge file need's
to be edit.

The really question I need answer is how can I see what changes
has been done in the master branch (the one pulled in) of the
file I suppose to merge manually. Is there no way to get out
the 2 last versions from the master branch and supply them to
KDiff3 or similarly diff program.

Also by reading the documentation I wounder what the difference is of:

- commit and check-in, seem to be same thing.
- update index-file and update the repository.

/Thanks