It's at a nice big pub with fancy beer and a stage for live music, so I'd guess it's a social event plus the companies introducing themselves from the stage so you know who to focus your mingling on.

Hmmm...as a graduate I really don't know how to equip myself at these kind of events. I wonder how I should go about fixing that

There's not a huge amount you need to do. It might be worth having a look at the sites of some of the companies listed so that you know vaguely who you want to talk to, but other then that, just turn up and make sure you have some way of taking down contact details for people - a pen and a notepad are probably your best option, unless you're particularly good at typing on a mobile phone keyboard.

The important bit is to talk to people once you get there, since it's unlikely that people are going to come and seek you out in the corner.