There are at least as many citation styles as there are journals; EndNote software includes over 6,000 styles!
When submitting a manuscript, you are responsible for finding out what citation style is required. This can be found by searching the journal's website (often called "Instructions for Authors") or by consulting your instructor/syllabus.
The following styles are the most commonly used in the health sciences:
Bibliographic management tools make it easy to maintain and cite references (and sometimes the articles themselves). They typically work with other software, such as Microsoft Word.