Hi Kamal,
Whenever if you want to import IDOC or RFC from ECC system we will goto this option.
Suppose if you want to do file to IDOC interface in SAP PI. we have to import IDOC into PI. So, in this case will go for Import Objects.
There you will give the system details like application server and system number of that system.
SUppose you want to import IDOC from ECC1 system. You have to give application server and system Number of that ECC1.
These details you will get from your basis team or ask the ABAPER.. he will provide to you..
https://help.sap.com/saphelp_erp2004/helpdata/en/2b/a48f3c685bc358e10000000a11405a/content.htm
Thanks,
Sreenivas.