Hi Amit,
If you using Excel add-in 2.4.4 to import your data. After you click button "Import to CA Agile Central", you should able to select the workspace and the work item type. And you should also see Validate button. Please click it the tool will auto check the what columns are you missing. Just like the Project and also some required fields.
If you are using Excel add-in beta New Excel Plugin - Open Beta
After you connect to the Agile central and go the import session. You should see the columns you need to ready.
I hope this help.
ZhaoKun