First of all in User control add events for all the controls
like in .ascx Page
<asp:Button id="btnSample" runat="server" onClick="btnSample_Click" Text="Test"></asp:Button>
in .ascx.cs page
private void btnSample_Click(object sender, EventArgs e)
{
}
After that just register that user control in the required .aspx page and in that .cs page just register the perticular event as per user control.