Molly Manning Walker sat at the Bushwick bar Mood Ring, attempting to dodge a karaoke request: “I’m not a singer,” she said apologetically. The filmmaker has worked with A$AP Rocky and won the Un Certain Regard prize at Cannes. “How to Have Sex,” her debut feature, opens this week. Manning Walker, 30, faced challenges shooting the movie in Crete, but drew from personal experience to convey the party scene dynamic. A traumatic experience led her to make a short film and later “How to Have Sex.” She hopes to create an action film and already has plans for a climate change project. After a brief karaoke performance from another patron, she observed and speculated on the nature of his date.