A patch is a file that show the differences between two revisions or between your local repository and the last revision your repository is pointing.
To share or save a patch of your local uncommitted changes either for peer review or to apply later, do:
svn diff > new-feature.patch
To get a patch from the differences between two revisions:
svn diff -r NEWER_REVISION:OLDER_REVISION > feature.patch
To apply a patch, run:
svn patch new-feature.patch
In order to apply the patch successfully, you must run the command from the same path where the patch was created.