This is how I use an update panel for a widget that I created.
<asp:DropDownList ID="ddlPayrollStores" runat="server" OnSelectedIndexChanged="ddlPayrollStores_SelectedIndexChanged" AutoPostBack="true">
</asp:DropDownList>
<asp:UpdatePanel ID="UpdatePanelPayroll" runat="server">
<Triggers>
<asp:AsyncPostBackTrigger ControlID="ddlPayrollStores" EventName="SelectedIndexChanged"></asp:AsyncPostBackTrigger>
</Triggers>
<ContentTemplate>
<div class="dragbox-content">
<asp:Label ID="lblLabelHours" runat="server" Text="Reg Hours: " Width="350px"></asp:Label>
<asp:Label ID="lblTotalHours" runat="server" Text=""></asp:Label>
<br />
<br />
<asp:Label ID="lblLabelOverTime" runat="server" Text="Total Overtime Hours: " Width="350px"></asp:Label>
<asp:Label ID="lblTotalOvertime" runat="server" Text=""></asp:Label>
<br />
<br />
<asp:Label ID="lblLabelHoliday" runat="server" Text="Total Holiday: " Width="350px"></asp:Label>
<asp:Label ID="lblTotalHoliday" runat="server" Text=""></asp:Label>
<br />
<br />
<asp:Label ID="lblLabelVacation" runat="server" Text="Total Vacation: " Width="350px"></asp:Label>
<asp:Label ID="lblTotalVacation" runat="server" Text=""></asp:Label>
<br />
<br />
<asp:Label ID="lbllableTotalHours" runat="server" Text="Total Hours: " Width="350px"></asp:Label>
<asp:Label ID="lblTotalStoreHours" runat="server" Text=""></asp:Label>
<br />
<br />
<asp:Label ID="lblLabelPay" runat="server" Text="Total Pay: " Width="350px"></asp:Label>
<asp:Label ID="lblTotalPay" runat="server" Text=""></asp:Label>
<br />
<br />
<div style="align-content: center">
<asp:LinkButton ID="lbDetailed" runat="server" Text="Detailed Report" PostBackUrl="~/Reporting/Payroll/StorePayroll.aspx"></asp:LinkButton>
</div>
</div>
</ContentTemplate>
</asp:UpdatePanel>
This is for a payroll widget that shows the store's total payroll. So when I select which store I want to see with the drop down, the update panel will post back without posting back the entire page. In my case, it will just display numbers as labels. Hopefully this leads you in the right direction and possibly clears it up a bit.