"PSHE" stands for "Physical and Social Health Education" (also sometimes called PSE) and is a compulsary subject for students in the UK until the age of 16, when it's replaced by "General Studies" (compulsary in most but not all schools and sixth form colleges). In PSHE you mainly study drugs (classification, laws about drug dealing and use, long and short term effects), and sex education (contraception, abortion, STDs, pregnancy). There's also some studying of religious beliefs, racism, time management, peer pressure, career decisions, etc.
"Citizenship" is now on the syllabus, and most schools use PSHE to "teach" us to be good citizens. According to www.teachernet.gov.uk , the aims of "citizenship education are to ensure that students "know their rights and responsibilities, understand and analyse significant issues, understand how society works, and play an active role in society".
Usually this subject is taught by giving students photocopied sheets from "Sugar" (a magazine aimed at teenaged girls that occasionally covers things like exam stress and anorexia), making them do spider diagrams (also known as mind mapping), making posters and presenting them to the class, and class discussions.
This subject is a great idea in principle, but teachers tend to forget that we've been force-fed information about smoking, alcohol etc from the age of six. We know it has unhealhy effects. We know it's important to eat a balanced diet, and exercise regularly, and so on and so forth. I'm in my first year of major exams, so my yeargroup is getting stressed about our workload. So we have a PSHE lesson in which we are played relaxing music. Most of us would find it more helpful to use this time on Private study, but that wouldn't be teaching us a valuable life lesson...