Directory permissions is not very clear

In the documentation you wrote :

For the application to work, some directories must be writeable by the web-server. On development server, this may be done by giving write permissions to all

chmod -R a+w <directory>

But the best way to do this on production server is to set the owner of the directory to the web server's process

chown -R www-data <directory> (provided www-data is the apache process owner, on some os, it is 'apache' or 'httpd')

Here follows a list of directories to set the permissions for. Those marked with a * MUST be writeable for the system to work, others must be writeable for automatic installation of plugins, but these steps can all be done manually: .... and that's what where it is not clear. Here's my question :

Those directories mentionned with a * at the end of their name (for the purpose of the explanation) must be writable. Now what does it mean ? Is it that some of these directories attribute will be change by chown -R www-data while other will be change by chmod -R a+w ?

Thanks

André