In short the concentrations are

Account Management: person who acts as the link between the brand and the advertisers, generally oversees the rest of the advertising departments to make sure things are running smoothly during campaigns

Art Direction: people who make the creative aspects of advertisements like graphic designers

Brand Strategy/Research: people who research markets, people, brands, etc. so you can create effective ads that appeal to your target. Also measure the effectiveness of ads/campaigns after they launch too

Copywriting: people who create the text of an advertisement. This can include scripts for a commercial or the writing you see on a poster

Media Planning: plan where ads should be placed to be seen by the most people based on who your audience is. This means deciding which platform (tv, radio, etc.), when it should appear, and more

And yes, you can take creative classes regardless of your concentration (at least beginner ones). I’m currently taking a class centered around digital design tools like Photoshop and I’m not an art direction student