Serial Number&WBS Element

Hi experts,

1-) I can not deliver sales orders because it requires serial numbers.

Can anybody tell me how to cancel asking serial numbers?

2-)If it is not available how can I create serial numbers?

I created serial numbers by trcode IQ01 but again I can not deliver sales order.

3-)At "create material serial number " screen it requires a WBS element.

What is WBS element?

And what is the role of it?

Thanks&Regards