For that you need to setup AIF. (End points, Action Policies , constraints etc.) if you are creating a new company - you can see in CEU company all these setup are being done.(you can see the AIF setup in that company).
After that create an item A001 in company A and create a company item B001 and attach it to the company item field
and now go to functions - click “Create item in company” where you can select the company B by checking include check box.
then it will automatically create B001 item in the company B.