Opportunity through BAPI

Hi,

I am a freelancer and currently working for SAP CRM where I am trying to create BAPI through FM. As we design, Lead will be created in third party system and I have to directly create Opportunities in SAP CRM system using FM. Could you guys, confirm me below points, as I am new to SAP CRM:

1. Can we directly create opportunity in SAP CRM, without Lead?

2. When I am trying to create Opportunity / Lead in SAP CRM system I am getting error "Document not saved" but nothing in error / log, what could be the expected cause ?

3. Also help me with documentation for using transaction CRMD_ORDER to create Lead and Opportunity.

Let me know if you any further info.

Thanks in advance.