The standard design contains basic functionality. The base templates contains the different functionality for the forum, image gallery and other things that are part of the packages.
They are used together, look at this: http://ez.no/doc/ez_publish/technical_manual/3_8/concepts_and_basics/designs/design_combinations
Tnx, but why do I also have a sitedesign called forum then? I'm confused of base, standard and forum..
The site-design is for you to customize so you do not need to do changes to the standard or base templates. Because of the template fallback mechanism, you can just make a similar structure in the forum design, and that template is used instead.
Example, you want to change design/standard/templates/user/login.tpl. Then you create the folder strucure desgin/forum/templates/user and add the template user.tpl there. Now this template will be used instead. (You need to clear the cache for eZ publish to find new templates.)
Now you know! If you want to, you can remove the base design.
However, i would not recommend it, because you are left with a very basic system. I normally use the article, folder, forum and so on from the packages.
