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).

f

Visit the file described on the current line, like typing C-x C-f and supplying that file name (dired-find-file). Visiting.

RET, e

Equivalent to f.

o

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. Windows.

C-o

Visit the file described on the current line, and display the buffer in another window, but do not select that window (dired-display-file).

mouse-1, mouse-2

Visit the file whose name you clicked on (dired-mouse-find-file-other-window). This uses another window to display the file, like the o command.

v

View the file described on the current line, with View mode (dired-view-file). View mode provides convenient commands to navigate the buffer but forbids changing it; View Mode.

^

Visit the parent directory of the current directory (dired-up-directory). This is equivalent to moving to the line for .. and typing f there.

@defopt dired-kill-when-opening-new-dired-buffer When visiting a new sub-directory in Dired, Emacs will (by default) open a new buffer to display this new directory, and leave the old Dired buffer as is. If this user option is non-nil, the old Dired buffer will be killed after selecting the new directory. This means that if you're traversing a directory structure in Dired, you won't end up with more than a single Dired buffer. @end defopt