在网站中单击电子邮件图标时打开电子邮件

I am creating a website now and one part of it is when the mail icon is clicked. The email interface will display. I've seen example in internet like below:

When the email icon is clicked. The email interface will show:

What I want to do is to apply it in my website but I don't have any idea how it works. I am here to asked some suggestions or link tutorials on how to do it or if it's possible a sample code. I'm using php codeigniter. Thank you.

you just need to add one <a> link and point to email like:

<a href="mailto:myemail@site.com?Subject=Some%20subject"><img src="myImage.jpg"/></a>