When you type ls, files beginning with a dot are not listed.
Traditionally, files that contain configuration information, user
preferences, and so on begin with a dot; these are hidden and out of
your way while you do your day-to-day work. Sample dot files are
~/.emacs, ~/.newsrc, ~/.bashrc, ~/.xsession, and ~/.fvwmrc. These
are used by Emacs, news readers, the Bash shell, the X Window
system, and the fvwm window manager, respectively. It is
conventional to end the dot filename with rc, but some programs
don’t. There are also directories beginning with a dot, such as
~/.gimp and ~/.netscape, which store preferences for the Gimp and
Netscape.
Sometimes a program will create a dot file automatically; for
example, Netscape allows you to edit your preferences with a
graphical dialog box and then it saves your choices. Other times you
will create them yourself using a text editor; this is the
traditional way to do it, but you have to learn the peculiar format
of each file—inconvenient at first, but it can give you a lot of
power.
To see dot files, you must use the -a option to ls. The long form of
-a is -all, if you find that easier to remember. You can also use -A
or -almost-all, which displays all dot files except . and ...
Remember that . is the current directory, and .. is the parent of
the current directory; because these are guaranteed to be in every
directory, there is no real reason to list them with ls. You already
know they are there.