Ccreate and apply a patch - Subversion

This is not recommended way to merge code with svn! 
 What are diff files ?
A diff file is the difference between a version of the source code in the repository and a working copy. It represents any changes, such as additional features or bug fixes, that have been made by a developer in a working copy. A diff file is generated using the svn diff command. To create a patch:

svn diff > svn_patch.diff

To apply the patch

patch -p0 -i svn_patch.diff

wath is patch command? 
patch takes a patch file patchfile containing a difference listing produced by the diff program and applies those differences to one or more original files, producing patched versions.

what -pX parameter means? 
 -pnum or --strip=num Strip the smallest prefix containing num leading slashes from each file name found in the patch file. A sequence of one or more adjacent slashes is counted as a single slash. This controls how file names found in the patch file are treated, in case you keep your files in a different directory than the person who sent out the patch. For example, supposing the file name in the patch file was.
 what -i parameter means?
 -i patchfile or --input=patchfile Read the patch from patchfile. If patchfile is -, read from standard input, the default.