Doing the following will generate a diff window.
:DirDiff <A:Src Directory> <B:Src Directory>
e.g.
:DirDiff ../something/dir1 /usr/bin/somethingelse/dir2
shortcut
]c : next diff
The following comamnds can be used in the Vim diff mode
\dg - Diff get: maps to :diffget<CR>
\dp - Diff put: maps to :diffput<CR>
\dj - Diff next: (think j for down)
\dk - Diff previous: (think k for up)