No. Some people are able to do it using instructions online, but having someone there to help guide you will certainly ensure you're doing it correctly and in the most effective way.
Are there different types of meditation?
Yes. Though they all follow the same sort of practice and have the same end goal of relaxation, there are different types, from different cultures, that are linked to different religions. If you're not really sure where to start, it's worth running a few searches online to really understand the differences and then chat to some course providers about which one will suit you.
What exactly does meditation involve?
It involves clearing your mind of stress and really focusing on relaxing. It's about mental concentration as well as making your body calm.
Do I have to wear anything special?
No, but it's usually best to wear something you feel really comfortable in so that you can really relax.
I want to learn to teach meditation but I've never tried it - is this possible?
Yes. You'll first have to learn how to meditate yourself and once you've mastered it, you'll be able to teach it to others. A course in teaching meditation will help you with this, though some may require that you can meditate yourself beforehand. Check with your course provider if you're not sure.