The idea is to encourage children to travel to school on their bikes. Cycling is good exercise and reducing car mileage has to be good for the environment; and it teaches children basic roadcraft. Moreover cycling is fun; it's something I wish I was still able to do.
Yes, if you're going to start cycling there are a few things you need to think about, but they're not difficult. Firstly, ensure that your bike is in good working order: check the tyres, lights etc. You should plan your route, so that you know exactly where you are going and what the road junctions are like — and always make sure that someone knows the route you will be taking. And last, not not least, be safe and wear a helmet.
Teachers!? No you're not excused; you're expected to join in. Bike to School Week isn't just for the kids!
Find more information on how to get started over at www.sustrans.org.uk/change-your-travel/children-and-families/schools/bike-school-week.