Not writeable

I have tried changing permissions for about eveything in my wordpress folders, but I still can’t edit theme or plugins. Also codeforged’s Headline Images plugin does not work. The plugin gives the error:

FATAL: The directory you specified to cache the image files is not writeable from the Apache task. Either select a different directory or make the directory you specified writable by the Apache task (chmod 755 the directory).

I am thinking it has something to do with apache … ? or some weird permissions thing. I’ve tried searching, and I’ve found nothing.

-shrimp