Jnicolas is asking about the different referencing styles - like Harvard (author/date), Vancouver (numbers in the text) that students need to use when referring to the sources they get their ideas from. It is important to reference correctly, otherwise you might be accused of plagiarism (copying ideas and not acknowledging them = cheating!).
At Queen Mary most departments use the Harvard system, except the medical school, which uses Vancouver.
I wish there was a universal system accepted across all universities, but this is not the case - not even across departments, or sometimes it just depends on the individual lecturer. If there is any doubt, just check with him/her as to which system they prefer their students to use.