Hi Todd
Thank you for contacting Syncfusion support.
You can find the UG documentation for creating and accessing form controls like text box, combo box, option box and check box from the below link.
UG Documentation link: http://help.syncfusion.com/file-formats/xlsio/working-with-drawing-objects#form-controls
Please let us know if you have any concerns.
Regards,
Dilli babu.