In this example we are going to pack two rectangles in a box, and have a separator in the middle.
So we start we the window, background, box and rectangle creation, all pretty normal stuff: 
#include <Elementary.h>
EAPI_MAIN int
elm_main(int argc, char **argv)
{
   Evas_Object *win, *bx, *rect, *separator;
   evas_object_size_hint_weight_set(bx, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   evas_object_show(bx);
   rect = evas_object_rectangle_add(evas_object_evas_get(win));
   evas_object_color_set(rect, 0, 255, 0, 255);
   evas_object_size_hint_min_set(rect, 90, 200);
   evas_object_size_hint_weight_set(rect, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   evas_object_size_hint_align_set(rect, EVAS_HINT_FILL, EVAS_HINT_FILL);
   evas_object_show(rect);
Once we have our first rectangle in the box we create and add our separator: 
   evas_object_show(separator);
- Note
- Since our box is in horizontal mode it's a good idea to set the separator to be horizontal too.
And now we add our second rectangle and run the main loop: 
   rect = evas_object_rectangle_add(evas_object_evas_get(win));
   evas_object_color_set(rect, 0, 0, 255, 255);
   evas_object_size_hint_min_set(rect, 90, 200);
   evas_object_size_hint_weight_set(rect, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   evas_object_size_hint_align_set(rect, EVAS_HINT_FILL, EVAS_HINT_FILL);
   evas_object_show(rect);
   evas_object_show(win);
   return 0;
}
This example will look like this: