Thank for all explanations. Now I understand:
So, you can say that Component Definition is the "blueprint" for an instance

If I make a model which I will need for further usage, I'll make it Component, to see it in Component Browser (and of course, I will save it in my Collection), but its inner components will be groups, otherwise my Component Browser will be filled up with all sort of C.Definitions that I don't need. Well, there are exceptions from this rule... But now is clear for me when to choose to use groups.

I have a structure like this:

--MAIN(component)
      |--COMPONENT
            |--GROUP

And, in GROUP, I want to access an attribute from MAIN. So, in GROUP I did this:

=MAIN!my_attr

,but it gave me the #
then I tried this way:

in COMPONENT;
-------------------
Attr = MAIN!my_attr
in GROUP;
--------
=COMPONENT!Attr

And this worked. But, from my point of view is kinda ugly to redefine at each level .
Is this normal? You can only access the parent's attributes, or it should be possible to access any attributes, no matter how high is the entity in hierarchy ?

So, my group has some extra, or loose edges or faces ? Hmm... I'm wondering if somehow this could be highlighted. In a intricate model is hard to discover where the evil is hidden .
But, i should not be worried, unless I use the Solid Tools, right?

Is there a way to change axis to a group? In sketchup I could not see any. Maybe a plugin? I looked over Plugins Index, but nothing kept my attention.
Or the only way is to make it component?
And talking about groups: is there any reason for using groups instead of (unique-at need) components? I'm a little confused... I don't know when to make entities group and when to make them components.

Hy ! I have Google Sketchup 8 PRO and I noticed something strange: in Entity Info, if I select a group (I was not aware if it happens to components too), sometime it shows "Group", other times it shows "Solid Group". Do you know what is the meaning of that?
Thank you.

@sketchdata said:

I attached a modified copy of your skp file with an "animation" on the drawer box, which will open the drawer guide in two stages one at 132mm and the other at 300mm. The drawer box bottom uses formulas, not a perfect DC for sure, but perhaps some formula examples you were looking for?

WOW Thanks a lot ! I'm glad it's working !
I can't understand much yet, but I'll study what you have done. At least, now I have a starting point.
If I will be able to refine your work, I will put it here (or should I put it on 3dwarehouse? ), so others to can access it.

Eventually, if I don't ask much, can you point some brief instructions about what to follow? Something like a "pseudocode", or schema if you know what I mean. Kinda "first you do this, second do that...". Because This is a really complex model for me And I'm afraid that I'l be lost between components.
Thanks again, sketchdata !

@dedmin said:

I struggled with the same problem and think that the dynamic components are not suitable for this. So, I made my drawers and resize with FredoStretch as needed.

Stretching would not be a problem. I tested something like that, see the Clothes Bar below. It stretches and the ends remain in position. I think same principle could be applied to the drawer, to be stretched... but what about the extraction? Extraction can be fun .

Dynamic Component: Oval Clothes Bar. It stretches and keeps sockets at ends.

I made this Dynamic Component after Some folks here helped me to figure out how . So, now I'm sharing it with you.
The drawer have several parameters:
Cabinet width - the width of cabinet where the drawer fits; 2Clearance will be subtracted from it to have Drawer's front width. Also, 2Cab. side thickness* will be subtracted in order to calculate drawer's width. I could ask just for inner width of the cabinet, but I thought is easier for user to input overall cabinet width and the code to do the math.
*Extraction length - how much you want to open the drawer
*Clearance - clearance around Drawer front (you can let more, if you use the dimensions for cutting, so later you can add edge stripes)
Front height - height of the drawer front; 2Clearance will be substracted from it.
*Front vertical offset - will displace the drawer front vertically (+/- from its default position)
*Cab. side thickness - thickness of cabinet's side panels

It's not perfect... but I did my best. If anyone have some suggestions of improvement, please tell me. As this is my first dynamic component that I made, I'm sure that it can be improved a lot.
the good one ! ...test it and come with suggestions !

######################################
Hello, I'm new here and the reason I joined the forum is that I need help with a dynamic component.
The problem is kind of wood-working related, but the real deal is about Dynamic Components, so I hope that I posted the topic in the right place.

I just started to play with dynamic components and for now is too difficult for me to make complex stuff. So, I'm hoping that somebody here will spare some time to make it for me and maybe, just maybe to give a short explanation about what he did, so in the future I will be more enlightened.

THE PROBLEM
It's about a drawer from BLUM, called METABOX. There are two types: with partial extraction (like most drawers, few centimeters stay inside the cabinet case) and there is one with full extraction, which come out (almost) completely.
This one is the full-extraction type. The main problem is that its rail is made from two segments, you will see in the SKP file attached.
So, the dynamic component must have two functions:
-to resize the width of the Drawer Bottom and Drawer Back accordingly with the inner size of the cabinet (overall width of the drawer assembly)
-to open the drawer(I guess if the two-segments rail can be solved, the single segmented one must be easier) - here I'm completely stuck. I have no idea about how to do it.

The 3D model was taken from BLUM DYNALOG Catalog and refined by me a little. If someone is interested, I can give you the catalog, or 3d models.

Thanks in advance.

skp file with the model and explanatory dimensions.