Tax Return question and W-2 form again

Please, what do i need when I the application? I heard I need previous 3-year tax returns and w-2 forms.
I was told I can order a tran of tax return from IRS. Is it just so called Return Tran? Is it enough?

And for W-2 forms, do I need a copy of each one or just a tran too? Or I even need an original one.

Thanks a million.