How To Start Fetchmail in Gnus Automatically?

[A. L.]

I am a newbie in Emacs and Gnus. I encounter some problems in using
Gnus, so go to here for some help.

The problem is that when pressing 'g' in Gnus I wish Gnus can
automatically call Fetchmail in background to download mails from
server, and thereafter Gnus can read them in spool.

Could some people can give me some advices for binding Fecthmail to key
'g' in Gnus or some other alternatives?

Thanks in advance.