This code places an Elementary file selector entry widget on a window, along with some other checkboxes. Those are there just as knobs on the file selector entry's state.

Here's how we instantiate it:

   ic = elm_icon_add(win);
   elm_icon_standard_set(ic, "file");
   evas_object_size_hint_aspect_set(ic, EVAS_ASPECT_CONTROL_VERTICAL, 1, 1);

   /* file selector entry */
   fs_entry = elm_fileselector_entry_add(win);
   evas_object_size_hint_align_set(fs_entry, EVAS_HINT_FILL, 0);
   elm_fileselector_path_set(fs_entry, "/tmp");
   elm_object_text_set(fs_entry, "Select a file");
   elm_object_part_content_set(fs_entry, "button icon", ic);

   elm_box_pack_end(vbox, fs_entry);
   evas_object_show(fs_entry);

Note that we set on it's button both icon and label decorations. It's set to exhibit the path of (and list the contents of, when internal file selector is launched) the "/tmp" directory, also, with elm_fileselector_entry_path_set(). What follows are checkboxes to exercise some of its API funtions:

   ck = elm_check_add(win);
   elm_object_text_set(ck, "editable selection");
   elm_check_state_set(ck, elm_fileselector_is_save_get(fs_entry));
   evas_object_smart_callback_add(ck, "changed", _current_sel_toggle, fs_entry);
   elm_box_pack_end(hbox, ck);
   evas_object_show(ck);

   ck = elm_check_add(win);
   elm_object_text_set(ck, "\"inwin\" mode");
   elm_check_state_set(ck, elm_fileselector_entry_inwin_mode_get(fs_entry));
   evas_object_smart_callback_add(ck, "changed", _inwin_mode_toggle, fs_entry);
   elm_box_pack_end(hbox, ck);
   evas_object_show(ck);

   ck = elm_check_add(win);
   elm_object_text_set(ck, "folders only");
   elm_check_state_set(ck, elm_fileselector_folder_only_get(fs_entry));
   evas_object_smart_callback_add(ck, "changed", _folder_only_toggle, fs_entry);
   elm_box_pack_end(hbox, ck);
   evas_object_show(ck);

   ck = elm_check_add(win);
   elm_object_text_set(ck, "expandable");
   elm_check_state_set(ck, elm_fileselector_expandable_get(fs_entry));
   evas_object_smart_callback_add(ck, "changed", _expandable_toggle, fs_entry);
   elm_box_pack_end(hbox, ck);
   evas_object_show(ck);

   evas_object_smart_callback_add(fs_entry, "file,chosen", _file_chosen, NULL);

The checkboxes will toggle whether the file selector entry's internal file selector:

must have an editable text entry for file names (thus, be in "save dialog mode")
is to be raised as an "inner window" (note it's the default behavior) or as a dedicated window
is to populate its view with folders only
is to expand its folders, in its view, in place, and not repainting it entirely just with the contents of a sole directory.

Observe how the entry's text will match the string coming from the "file,chosen" smart event:

/* hook on the file,chosen smart callback */
static void
_file_chosen(void        *data EINA_UNUSED,
             Evas_Object *obj EINA_UNUSED,
             void        *event_info)
{
   const char *file = event_info;

   if (file)
     printf("File chosen: %s\n", file);
   else
     printf("File selection canceled.\n");
}

Whenever you dismiss or acknowledges the file selector, after it's raised, the event_info string will contain the last selection on it (if any was made).

Try, also, to type in a valid system path and, then, open the file selector's window: it will start the file browsing there, for you.

See the full source code for this example.