Email to Calendar.applescript

#################################################################################
# Title: Create Calendar Event from eMail 
#################################################################################

# Iain Dunn
# Logic2design.com
# logic2design@icloud.com

## v3 - added AllDay event

#################################################################################
# Configuration
#################################################################################

#Set Current Date & Time
set todayDate to current date
set eventDate to short date string of todayDate as text
set eventTime to (do shell script "date +\"%l:%M %p\" | awk '{$1=$1;print}'")

#Event Time
display dialog "When is the Event?" default answer eventDate & " " & eventTime
set theStartDate to date (text returned of result)

display dialog "How long is the Event? (minutes)
 
Set to 0 for an all day event" default answer 30
set appt_length to text returned of result
if appt_length < 1 then
	set appt_mins to (0)
	set theEndDate to theStartDate + (appt_mins * minutes)
	set allDay to true
else
	set appt_mins to (appt_length)
	set theEndDate to theStartDate + (appt_mins * minutes)
	set allDay to false
end if

#################################################################################
# Script
#################################################################################

#get eMail
tell application "Mail"
	set theSelection to selection as list
	# do nothing if no email is selected in Mail
	try
		set theMessage to item 1 of theSelection
	on error
		return
	end try
	
	set theSummary to theMessage's subject
	set theDescription to theMessage's content
	set theOrigMessageId to theMessage's message id
	set theUrl to {"message:%3C" & my replaceText(theOrigMessageId, "%", "%25") & "%3E"}
end tell

#select Calendar
tell application "Calendar"
	set clist to name of calendars
	set cname to choose from list clist with prompt "Select Calendar"
	set cal to cname as text
	
end tell

#Create Event
tell application "Calendar"
	tell calendar cal
		make new event with properties {summary:theSummary, description:theDescription, url:theUrl, start date:theStartDate, end date:theEndDate, allday event:allDay}
	end tell
end tell

tell application "Calendar" to activate
#################################################################################
# Functions
#################################################################################

# string replace function
# used to replace % with %25
on replaceText(subject, find, replace)
	set prevTIDs to text item delimiters of AppleScript
	set text item delimiters of AppleScript to find
	set subject to text items of subject
	
	set text item delimiters of AppleScript to replace
	set subject to "" & subject
	set text item delimiters of AppleScript to prevTIDs
	
	return subject
end replaceText

Where do I have to put the code in order to work?