A typical class will start with a 10-minute warm-up, followed by about half an hour of boxing and finishing with a 10-minute warm-down. Classes will teach you how to punch properly — it's about technique not strength.
There are three main moves to employ: hooks ("side" punches), jabs (straight forward punches) and up-cuts (punches going upwards). Your instructor will tell you which combinations you'll be doing, and may also get you to change partners part-way through the work-out.
Don't think that boxing is an easy ride, though: it's seriously hard work. Boxing is a high intensity, full body workout that will keep you moving the whole time. When you're not throwing a punch, you're ducking and weaving — or doing squats and abdominal work.
I've never boxed in my life. Will I be able to do it?
Boxing is all about technique so once you pick up the moves you should be fine. If you're not particularly fit then that's not a huge problem. Boxing is actually easier for a lot of people than running, especially for those with excess weight. It's easy to modify the exercise to suit you so everyone of all ages and fitness levels can participate.
It's not just a sport for the guys either; women actually pick up the combinations faster than men and have more flexibility through their mid-section. The rotation of the back is where all the strength comes from for a punch, not the arms.