--autounmask tells emerge to show you what you should add to your package.accept_keywords in order to unmask masked packages.
--autounmask-write tells emerge to automatically modify package.accept_keywords and package.use. You still need to apply the changes using dispatch-conf, since Portage's config files are protected by CONFIG_PROTECT.
{,-write} tells bash to duplicate the argument, adding to the first argument and -write to the second.