In The TV Show:
Stefan and Elena met at school on the first day back from summer,Stefan was a new student and Elena had went there before the summer.
The first time she saw him was when he was at the office checking in,her and her best friend Bonnie only saw his back,before Elena could see him turn around she saw her little brother,Jeremy,go into the boys bathroom and follows him in.
The second time she sees him is when she walks out of the bathroom after talking to Jeremy,they almost bump into each other and says a few words,stared at each other and then went their separate ways.
The third time she sees him is when she's in the cemetery visting her parents grave,she was writing in her journal when a black crow comes out of no where and sits on the headstone.She gets freaked out and runs out leaving her journal on the ground,she falls down a hill and gets a little cut.At the bottom of the hill was Stefan.