Groups and Ladder groups help

I know, i know .. this is probably something i should know but ...
Can anyone explain me (or point me to an external resource) what a newly introduced Ladder groups serve for (and that we didn't have in previous forum versions).
Any practical example on how to set this up?

Sorry for what is probably a basic forum knowledge .. but it seems i'm getting too old too fast

Thanks Bruce;

unfortunately, i still don't know what's the difference between what we had in the past from what we have now except that we have ladder thing.
Are ladder groups as kind of possible "subgroups" ?

p.s.
the reason i'm asking is that i need to explain the changes to our members but i'm confused myself 

WebWiz-Bruce wrote: If members do move up groups depending on how many posts they made then leave the ladder groups as they are, you only need to use multiple ladder groups feature if you want more than 1 group system for moving members automatically between groups based on their points.

That's it .. now i get it (finally)

No I think you are completely missing the point.

In version 9 you have 1 ladder system which groups could be part of. Members who were in groups that are part of the ladder system can move up groups depending on point count.

Version 10 is exactly the same as this and your present ladder system would be carried across. Where version 10 does differ is that you can create a second, third, forth, etc. ladder systems and place different groups in these new ladder systems.

A member group can either not be a part of the ladder system, or if you place the group in a ladder system it can only be in one ladder system. You can not have a member group that is part of multiple ladder systems.