However, I have no idea about where I can insert the code which is introduced in this website.
I can open the folder of Front end PM.
I guess that I can insert the cord to “/wp-content/plugins/front-end-pm/templates/newmessage_form.php”.
However, where can I insert the introduced code in the file?
Suppose you are writing a blog post and now you want your users to send a message to you about that blog post. You can add this link in that blog post. Now when a user will click that link they will redirect to message page with your name in the “To” field so that they will not need to search your name. They can just write subject and message and send to you.