A line for each article is displayed in the summary buffer. You can move around, read articles, post articles and reply to articles.
The most common way to a summary buffer is to select a group from the group buffer (see Selecting a Group).
You can have as many summary buffers open as you wish.
You can customize the Summary Mode tool bar, see M-x customize-apropos RET gnus-summary-tool-bar.
The key v is reserved for users. You can bind it to some command or better use it as a prefix key. For example:
(define-key gnus-summary-mode-map (kbd "v -") "LrS") ;; lower subthread