SQL DESCRIBE was( SQLRPGLE - Dynamic selection)

Hi Russell,
I am fairly familiar with SQL, but one thing eludes me.
I read the manuals, thats where I get my information
but I just cannot comprehend what the SQL DESCRIBE is
for. (Incidently the SQL manuals require that I bend
my brain into the 4th dimension before I grasp even the
slightest glimmer, but at least we have documentation.)
I dont know what DESCRIBE does nor have I ever had a
need to use it. If I knew what it did I probably would
use DESCRIBE.
If possible can I ask you to give me your understanding
of what DESCRIBE is and how to use it.

Yous in hope,
Frank Kolmann

***************  REPLY SEPERATOR ****************
from: Russell Conerly <rconerly@xxxxxxxxxxx>
subject: Re: SQLRPGLE - Dynamic selection

Here's a snippet...
     eval      statement = 'Select '
               + %trim(Field1) + ','
               + %trim(field2) +
               ' from ' + %trim(filename)
C/EXEC SQL
C+ PREPARE SQLSTMNT FROM :statement
C/END-EXEC

C/EXEC SQL
C+ DESCRIBE SQLSTMNT INTO :SQLDA USING ALL
C/END-EXEC

C/EXEC SQL
C+ DECLARE A1 CURSOR FOR SQLSTMNT
C/END-EXEC
...etc.
Hope this helps.
Russell Conerly