If you want to create report for the session model ,first you have to move on .py file and setup all dependencies module. And For each session, it should display session's name, its start and end, and list the session's time date and unique number.
For example you can see below code.

<openerp>
<data>
    <report id="report_session" model="openacademy.session" string="Session Report" name="openacademy.report_session_view" file="openacademy.report_session" report_type="qweb-pdf">

    <template id="report_session_view">
        <t t-call="report.html_container">
            <t t-foreach="docs" t-as="doc">
                <t t-call="report.external_layout">
                    <div class="page">
                        <h2 t-field="doc.name">
                        <p>From <span t-field="doc.start_date"> to <span t-field="doc.end_date"></span></span></p>
                        </h2><h3>Attendees:</h3>
                        <ul>
                            <t t-foreach="doc.attendee_ids" t-as="attendee">
                                <li><span t-field="attendee.name"></span></li>
                            </t>
                        </ul>
                    </div>
                </t>
            </t>
        </t>
    </template>
</report></data>
</openerp>