In some cases SMF will ask you to provide an FTP path. Your FTP path is the actual location of your files in your site. It is similar to the path used in your personal computer i.e. c:\windows\mydocuments\. It is formatted differently in Unix system ex. /public_html/forum/.

If you FTP to your site using SmartFTP, you will probably see something like this:
mail
public_html
public_ftp
tmp
www

If you browse to public_html the location will be /public_html/ and it may contains some sub folders:
cgi-bin
forum
include

If you browse to forum the location will be /public_html/forum/.