at new years eve there's a karaoke and troy Bolton[played by Zac Efron]and Gabriella [hows played by Vanessa] get picked... they sing start of something new.But when the school turn has started they meet again.. Troy is quickly in love but everyone else doesn't understand how there in love because Troy is in the cool gang and has Sharpay/rich girl [hows played by Ashley tisdale]is in love with Troy.there friends try to split them up and it works but it works out in the end.
A little more detailed answer...
At a New Years Eve party on Christmas break, Troy (played by Zac Efron) and Gabriella (played by Vanessa Ann Hudgens) are paired together to sing a duet. Both are reluctant in the beginning, but they seem to have a connection during the song. They talk afterward, exchange phone numbers, but fear they'll never see each other again. On the first day back at school, Gabriella is shown walking through the halls with her mother talking about not wanting to go to yet another new school. Her mother promises not to move the family again. Troy and Gabriella are stunned to see one another, yet very happy. Their friends don't understand the friendship, he being a popular jock and her being a smart, shy girl. She talks him into joining the musical, and the rest of the movie is them working through obstacles trying to hold them back. Attempting to win Troy's attention is Sharpay (played by Ashley Tisdale), the popular diva of the school. All in all, it's a great movie. Definitely a Disney Chanel Original, but entertaining, nonetheless.