The enormous NHS Direct website is a mine of practical useful information on everything in this section (so we often send you to bits of it) go to http://www.nhs.uk/Pages/homepage.aspx and start clicking
You should know roughly How your Body Works – what the kidneys are for, what meat is, what happens to a broken bone etc – so at least you know when something’s wrong. And it’s handy knowing (and so not worrying) about Common Illnesses and their treatment. And knowing the services you can call on – How the NHS Works and how to use the other practitioners like Dentists, Opticians etc.
A basic understanding of Healthy Eating - nutrition, food and cooking - allows you to give yourself a healthy balanced diet and to avoid dependency on junk food
Then the things that you can do to help yourself – proper Exercise, why Smoking is a really bad idea (you’ll DEFINITELY die younger and be more miserable – no kidding), sensible Drinking, not letting Drugs ruin your life, simple but important stuff on Keeping your Teeth and basic First Aid so you don’t panic in accidents.
Do we want to go into good mental health? Yes we do at least a bit. Being Happy is all about the positive things that we can do – not woolly spiritual nonsense but straightforward things to do like Cognitive Behaviour Training to avoid depression without pills and de-cluttering your life. This stuff really can put years on your life – and good happy years. There is no reason not to have a full and happy life – you just have to make it happen.
If you have some specific condition like Asperger’s Syndrome or a physical disability there is no need to let it destroy your life. There was a wonderful quote somewhere (I’d attribute it if my memory wasn’t going!) about the contributions made by Lord Nelson, Winston Churchill or Stephen Hawkins (respectively partially blind, subject to depression and completely disabled). We could all just be sorry for you but it is much better if you tackle your own difficulties and you can start by looking in Handling Disability