I'm brand spanking new to this site, trying to figure it out and I notice that I can select only one category in which to work.
My CV is kind of eclectic, I've worked in PR, Advertising, Sales&Marketing, Customer Service, Translation, I've touched a bit of everything and I thought that I could offer my services in all of these areas.
Is it possible to do this on Upwork?
Yes, you can look for jobs and work in any category you want to. You can also list different skills in your profile. BUT. I don't advise that. You'll spread yourself too thin. Clients may not like to see so many different skills. I would, IMO start off with just 1 or possibly 2 skills and concentrate on jobs which require those skills. Later on, when you have a few jobs completed, you can expand of your skills and job searches.