Attention will be paid to whether you sit quietly or dominate, whether you contribute constructively or destructively, and whether you're logical or emotional. Employers will look at the role you play - some people are best at the ideas stage, others at pushing things towards a conclusion. It's rare for employers to be looking for just one sort of person. Any team needs people with a variety of skills so try as much as possible to be yourself. You may have to give a presentation.
Topics vary widely.
You could be asked to talk about a personal interest or something directly related to the organisation. Most people worry about giving presentations but a few simple rules will help you through. Talk to the audience and not your notes, and scan everyone while you're talking rather than just addressing one person. It's also a good idea to check that you're comfortable with the equipment before you start. Scan the audience.