How to set Org_id at back-end

How to set Org_id at back-end 
We have a API to set the org_id from the backend. 

begin 
fnd_client_info.set_org_context(); 
end; 

Note:- Org_id indicates the "Operating Unit" in the Business Structure. 
How to I know what Org_id is set at back-end 
We can use userenv function to know the Org_id set at backend. 
select userenv('CLIENT_INFO') from dual; 

Why we need to set org_id at back-end 
We usually, set org_id at back-end. So that we can get the org_id records from the Multi Organization views. 

Above is applicable only till 11i version. It is different in Release 12.