Here's why Quirrell touches Harry:
* Lord Voldemort is possessing Quirrell: Quirrell is being controlled by Lord Voldemort, who is clinging to the back of his head. Voldemort is trying to steal the Sorcerer's Stone from Harry.
* Voldemort needs to touch Harry: To steal the Stone, Voldemort needs to touch Harry's forehead. This is because the Stone is protected by a powerful magical barrier that only Harry can pass.
* Quirrell's touch is meant to distract: The touching is a way for Voldemort to get close to Harry and distract him while he attempts to steal the Stone.
It's important to note that Quirrell is not actually trying to harm Harry in that moment. His goal is to get the Stone, not to hurt Harry directly.
Let me know if you have any other questions about the books or movies!