There are several Dired commands for visiting or examining the files listed in the Dired buffer. All of them apply to the current line's file; if that file is really a directory, these commands invoke Dired on that subdirectory (making a separate Dired buffer).
Visit the file described on the current line, like typing C-x C-f and supplying that file name (dired-find-file). Section 16.2.
Equivalent to f.
Like f, but replaces the contents of the Dired buffer with that of an alternate file or directory (dired-find-alternate-file).
Like f, but uses another window to display the file's buffer (dired-find-file-other-window). The Dired buffer remains visible in the first window. This is like using C-x 4 C-f to visit the file. Chapter 18.
Visit the file described on the current line, and display the buffer in another window, but do not select that window (dired-display-file).
Visit the file named by the line you click on (dired-mouse-find-file-other-window). This uses another window to display the file, like the o command.
View the file described on the current line, using M-x view-file (dired-view-file).
Viewing a file is like visiting it, but is slanted toward moving around in the file conveniently and does not allow changing the file. View File.