I will do my best to explain some things.

> Simple commands work, using 'Apply' from the 
> Procedure Browser screen, like; 
> => (gimp-version)
> ("2.2.8")

Note that the return value is a LIST containing the string "2.2.8". All
PDB functions return a LIST of items even if that list only contains one
item (indeed, the majority of the query-type commands return a one-item
list; requiring '(car ret-value)' to access the item itself).

> >From there on, I have difficulty understanding the 
> Return Values, and the requirements for the 
> function parameters suchs as; CHANNELS, 

IMAGEs, CHANNELs, DRAWABLEs, LAYERs, DISPLAYs, et cetera are all integer
 IDs which are unique within their group (you might have an IMAGE with
an  ID of "3" and LAYER with an ID of "3", but you will never have two
layers with an ID of "3" at the same time). They would all seem to be
non-negative integers greater than zero (I think it is a fair assumption
that this will always be the case).

DRAWABLEs are a superset of LAYERs, CHANNELs, and LAYERMASKS. 

A LAYER is an arbitrary-sized bitmap that can be either RGB or
GRAYSCALE. By arbitrary-sized, I mean that its dimensions are not bound
by the image dimensions (nor is its position, a LAYER can be completely
"outside" the image).

A CHANNEL is a fixed-sized, GRAYSCALE bitmap whose dimensions are fixed
and whose position is anchored. If the CHANNEL is a LAYERMASK then the
size and position are the same as the the LAYER to which it belongs.
Otherwise, the CHANNEL's size and dimensions are the same as the IMAGE's.

These identification numbers are what is expected (and what are
returned) when you see them referenced in the PDB. They are simple
integers (i.e., they are NOT pointers or structures) and you can specify
 them explicitly as such in the Script-fu console. For example:

(gimp-image-get-active-layer 1)

Will return the active layer for IMAGE "1" (the IMAGE-ID, "1", is
assigned to the first image you open with the GIMP)

> Like in the following, which the Procedure Browser 
> says should be; 
> num_images INT32  The number of Images open
> image_ids  INT32ARRAY  The list of images currently open
> => (gimp-image-list)
> (1 #(2)#1"02")

The LIST returned contains two items: the second item is an array of
active IMAGE-IDs and the first item is the size of the array. To access
an entry in the array, use 'aref':

(define all-images (gimp-image-list))
(define first-image (aref (cadr all-images) 0))
(define last-image (aref (cadr all-images) (- (car all-images) 1))

The value of an IMAGE-ID is appended to the filename in the window's
titlebar; which makes interaction from within the console easier. For
example, "Untitled.png-#1.0" in the titlebar indicates that the IMAGE-ID
is "1" (the "0" indicates the DISPLAY-ID, and will be zero unless you
have more than one view open for the same image).

> If someone could give me an example of using the 
> Script-FU Console to work gimp-drawable-set-pixel  
> that would be great.

In order to use 'gimp-drawable-set-pixel', you must create a byte-array
for the pixel's color. This can be accomplished with the following function:
(define (color-as-bytes r g b a) 
  (let* ((color (cons-array 4 'byte)))
    (aset color 0 r) 
    (aset color 1 g)
    (aset color 2 b)
    (aset color 3 a))

Once that function is defined (and assuming that my description of
drawables wasn't completely unfathomable), you would use the following
command to set a pixel on an RGB drawable:

(gimp-drawable-set-pixel drawable 1 1 4 (color-as-bytes red blue green

Note that you will see no change in the display; even if you were to
perform a 'gimp-displays-flush'. The set-pixel command does not register
with the UNDO history (it might be problematic to UNDO a few million
pixel ops) and therefore you must manually force an update to the
display to see the change (I would recommend hiding-and-unhiding the layer).

"It is amazing what you can accomplish if you do 
not care who gets the credit." -- Harry S. Truman

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