Daniel, to answer the first part of your question, the answer is no, you do not "have" to use a stabilser, but it is a very sensible thing to do, especially if you have never towed a caravan before.
To answer your second part, YES there is a raft of laws covering towing, which if you have not already investigated is a very unwise thing to have done, or not done.
Just a couple of things to start with:
Is your car legally capable of towing the van you have bought?
Is the train weight of the whole outfit within the legal limits as set by the car manufacturer?
Is the van you have bought of a legal size to be towed by your tow car?
Is the van in a roadworthy state to be towed?
Is your driving licence categorised to allow you to tow?
Have you informed your car insurance company that you will be towing?
Do you have insurance in place should your van damage another vehicle or person if it becomes detached from the car?
Some info about what you have bought and what tow car would be helpful to give a more informed information to you.