If it is working, it's just what you asked your friend for.
Why don't you ask your friend?

Next time, be more precise which part you do not understand instead, thanks.

Code:

#!/bin/bash

Use bash explicit as interpreter to run this script

Code:

START="a.txt"
END="b.txt"
DIFF="c.txt"

Define 3 variables with a file name.

Code:

mv ${START} ${END} #moving the first file to be compared

Renames the start file to the name of the end file. If it already exists, it is overwritten. Saves the data in the file from the previous run to b.txt so they are not lost and can be compared with actual data.

Code:

find /home -type f -mmin -5 -print > ${START}

Find files in directory /home that are not older than 5 minutes and write their path and name into the file a.txt.

Code:

diff ${START} ${END} | grep '<' > ${DIFF}

Find the lines that are different from the old file b.txt and write them to the file c.txt.

Code:

COUNT=$(cat ${DIFF} | wc -l)

Count the number of different lines.

Code:

if [[ -s ${DIFF} ]] ; then
     cat -- ${DIFF} | mail -s "Modified files in last 5 minutes *** ${COUNT} ***" root
fi

Check if the file c.txt exists and has a size greater 0.
If this is the case, tell cat to not accept any switches and send a mail with the subject "Modified files..." where the mail's body is the cat'ed different lines to root.