To summarize the Pretty Little Liars pilot episode, let's go through each character we meet. Events all take place a year after Alison disappears from the town of Rockwood. The incident takes place during a sleepover with her friends, and viewers catch up with them on this premiere...
ARIA: Just returning town after a year away, due to her dad's job. She quickly learns from Emily that the girls all drifted apart after Alison vanished. She also discovers that her new English teacher (Ezra Fitz) is the same guy she met and made out with at a restaurant the day before. Awkward! She later confronts him and he makes it clear they can't see each other, but Aria clearly wants something between them to continue. (And it does, when they make out again at Alison's funeral! More on that below.)
She later gets a text from someone that claims to know Aria and Fitz made out. This same individual makes a comment about Aria's dad's affair, as viewers are treated to a flashback that shows Aria and Alison catching the former's father in the fact. He knows that Aria knows, but Aria's mom is clueless. The text in question is signed by "A."
HANNA: She's taken over as alpha girl in school with Alison gone. She's also grown very tight with Mona, a girl that used to be a major nerd. These two often shop lift together, which results this week in Hanna getting talk. But shady, protective mom to the rescue! Hanna's mom works out a deal with the poloce to not file any charges, and Hanna later sees what that is: her mom sleeps with the cop.
Hannah also receives a text from A. It refers to eating food in prison, as Alison used to mock Hanna for her weight.
SPENCER: She has problems with her sister, Melissa. The latter comes home, introduces the family to her fiance (Wren) and takes over the barn/apartment Spencer had been promised by their parents. A lot of jealousy issues here. Spencer and Wren get along very well, as the latter even gives the former a massage. This leads to A's email to Spencer, which warns her not to make a move on Wren because "you kiss, I tell."
EMILY: She seems the most normal of the group, so to speak. She quickly befriends a girl named Mona, who moved into Alison's house. There's an odd, quicl lesbian vibe between these two. Emily receives a hand-written letter from A, one left in her locker. It refers to an incident back in the day when Emily and Alison kissed.
Now that we've met the girls, here's where we are at the end of the episode: Alison's body is found! Workers found it under the town gazebo. There's a funeral, at which the quartet is seated together and they all witness a girl named Jenna enter. She appears to be blind. Multiple times through the episode, there were references to the "Jenna thing." All girls seem worried when they see her now.
They get more worried when a detective approaches them and says he's gonna get to the bottom of Alison's death. The final scene of the pilot? All four girls get a text from A. It reads: "I'm still here, bitches. And I know everything."