Hello.

There is 16 handlers you can use for your bizform. You can see them if you open Kentico solution in your Visual Studio, open /WebParts/BizForms/bizform.ascx, switch to Design mode, go to its Properties -> Events.

If you want to access particular field or check its value, you can do it using this API:
BizForm.BasicForm.FieldControls["Example"];, where BizForm is code-name of your bizform and "Example" is the name of appropriate field.

For example, if you want to get a value of e-mail field, you can use this code:
CMS.FormControls.FormEngineUserControl em1 = (CMS.FormControls.FormEngineUserControl)BizForm.BasicForm.FieldControls
["Email"];

You can also use Form control in bizform´s field and use any custom logic in code-behind of this form control.

Best Regards,
Radek Macalik