How do I navigate in the results of Diff
Next line : return
Next page : space bar
Previous page : w
Quit viewing the diff : q
Help : h
Hit ? and it should show you the command shortcuts for doing page up/page down etc.
By default git looks at the $GIT_PAGER, then $PAGER environment variable to determine the program to be used for showing you the output of diff, log, show etc.
On new (linux) systems the default $PAGER used (even when it is not set) is less (it used to be the less capable more).
In both less and more the ? key gives you a command shortcut list.