Add a paragraph explaining events and signals

docs/reference/gtk/getting_started.xml

@@ -12,6 +12,9 @@
   <link linkend="gtk-compiling">Compiling the GTK+ libraries</link>
   section in this reference.</para>
 
+  <section>
+    <title>Basics</title>
+
     <para>To begin our introduction to GTK, we'll start with the simplest
     program possible. This program will create an empty 200x200 pixel
     window:</para>
@@ -83,8 +86,15 @@
 
     <para>The last line of interest is the call to gtk_main(). This function will
     start the GTK+ main loop and will block the control flow of the
-  <function>main</function>() until the gtk_main_quit() function is
-  called.</para>
+    main() until the gtk_main_quit() function is called.</para>
+
+    <para>While the program is running, GTK+ is receiving
+    <firstterm>events</firstterm>. These are typically input events caused by
+    the user interacting with your program, but also things like messages from
+    the window manager or other applications. GTK+ processes these and as a
+    result, <firstterm>signals</firstterm> may be emitted on your widgets.
+    Connecting handlers for these signals is how you normally make your
+    program do something in response to user input.</para>
 
     <para>The following example is slightly more complex, and tries to
     showcase some of the capabilities of GTK+.</para>
@@ -104,5 +114,6 @@
         </xi:include>
       </programlisting>
     </example>
+  </section>
 
 </chapter>