Let me google that for you (http://lmgtfy.com/?q=how+are+stars+formed)

Julie - you asked this question in the homework help section, and therefore you are expected to do some work to try and find an answer yourself. The link I gave you leads to lots of information about star formation, including the very first link which has an excellent explanation:
Stars - NASA Science (http://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve/)

If after reading the information on that site you have a specific question about star formation please ask. But it is inappropriate to indicate that a response is "not helpful" unless the information provided is factually incorrect. Clearly that is not the case with my earlier response!