Copy and Paste from the Gnus FAQ
I don’t like the layout of summary and article buffer, how to change it? Perhaps even a three pane display?
You can control the windows configuration by calling the function gnus-add-configuration. The syntax is a bit complicated but explained very well in the EmacsManual InfoMode node “Window Layout”. Some popular examples:
(gnus-add-configuration '(article (vertical 1.0 (summary .35 point) (article 1.0))))
(gnus-add-configuration '(article (horizontal 1.0 (vertical 25 (group 1.0)) (vertical 1.0 (summary 0.25 point) (article 1.0))))) (gnus-add-configuration '(summary (horizontal 1.0 (vertical 25 (group 1.0)) (vertical 1.0 (summary 1.0 point)))))