Learning to use X11

When I started programming many years ago, on a system very, very different from what we use now, producing graphical output from programs was easy;
all the necessary commands were usually built right into the language. Later, when I moved to C and UNIX, things were no longer simple. Not only does
C not include any graphics manipulation functions, per se, but all graphical output in UNIX has to go through the standard UNIX windowing system: the
X Window System, release 11, version 6.6 (its current incarnation), or X11 for short.”