It’s quite easy to use Gnus to read your new mail. You just plonk the
mail back end of your choice into gnus-secondary-select-methods,
and things will happen automatically.
For instance, if you want to use nnml (which is a “one file per
mail” back end), you could put the following in your ~/.gnus.el file:
(setq gnus-secondary-select-methods '((nnml "")))
Now, the next time you start Gnus, this back end will be queried for new articles, and it will move all the messages in your spool file to its directory, which is ~/Mail/ by default. The new group that will be created (‘mail.misc’) will be subscribed, and you can read it like any other group.
You will probably want to split the mail into several groups, though:
(setq nnmail-split-methods
'(("junk" "^From:.*Lars Ingebrigtsen")
("crazy" "^Subject:.*die\\|^Organization:.*flabby")
("other" "")))
This will result in three new nnml mail groups being created:
‘nnml:junk’, ‘nnml:crazy’, and ‘nnml:other’. All the
mail that doesn’t fit into the first two groups will be placed in the
last group.
This should be sufficient for reading mail with Gnus. You might want to give the other sections in this part of the manual a perusal, though. Especially see Choosing a Mail Back End and see Expiring Mail.