There are three functions you can use to open a custom screen:
openscreen(), openscreentags() or openscreentaglist().  prior to release 2
(V36), OpenScreen() was used to create a new screen.  With V36 and later
versions of the operating system, this call is superseded by
OpenScreenTagList() and OpenScreenTags().

   struct Screen *OpenScreen( struct NewScreen *)
   struct Screen *OpenScreenTagList( struct NewScreen * , struct TagItem *)
   struct Screen *OpenScreenTags( struct NewScreen *, ULONG, ULONG, ... )

The old openscreen() call relied on a fixed size data structure
(newscreen) which made little allowance for extensions and growth.  the
new calls are tag based, allowing for the addition of new features without
modification of existing structures and applications.  The
"screen attributes" section below contains a complete list of all the tag
options available for setting up an Intuition screen.  For a general
description of tag items, see the "utility library" chapter.

 a custom screen example 
 creating a custom screen that works with older systems 
 return values from openscreentaglist() 
 closing the screen