To be able to open an email client with prepopulated data you can either use the following html syntax so that user would click the link an dialog gets opened or the code within the code window.
<a href="mailto:user@test.com?subject=Test Subject&body=Dear admin,%0D%0AWe would like to buy the following products;%0D%0A%0D%0A1kg Apple%0D%0A1kg Orange">Send email</a>
Email should be placed right after the mailto:
Subject should be placed after subject=
Body should be placed after the body=
To have newline within body content you can use %0D%0A .