braindead user

hello,
i'm a braindead user :cry: hence i need to ask:

what is the purpose of the file that goes in the
'private key file' box ?

what type of file should it be ?

why do i want to know ?

because i'm trying to use winscp to upload a site (which actually doesn't
exist yet) to sourceforge...... or my ntl webspace
how's that gonna work?
it won't of course
what i should say is i'm intending to upload my site in the future

plz help

will