When Winnie Foster first comes across Jesse Tuck, he is drinking from a spring. Winnie has been feeling a bit dissatisfied with her life, so it's pretty exciting that she's meeting a cute boy here, in her woods, drinking from her stream.
Naturally, she wants to join him and drink too. Jesse Tuck, however, refuses to let her, without giving any explanation and becoming much more serious. Of course this is suspicious, and the stream belongs to Winnie's family in the first place, but they are interrupted when Mae Tuck (Jesse's mother) and Miles Tuck (Jesse's brother) show up, talking about danger.
This is the inciting incident of the story, the moment that starts off Winnie's big adventure. From here, she will learn about the Tuck family and come to decide whether or not she wants to drink from the stream as well.