The basic - and minimal - structure of an email template looks like this:
<record id="your_mail_template_id" model="mail.template">
<field name="name">Name of your template, shown under email templates</field>
<field name="model_id" ref="base.model_res_partner"></field>
<field name="email_from">${object.user_id.email_formatted |safe}</field>
<field name="partner_to">${object.id}</field>
<field name="subject">Title of email being sent</field>
<field name="body_html" type="html">
<div style="margin: 0px; padding: 0px;"> Your email text comes here. </div>
</field>
</record>