As a kid, Ariana Grande loved singing karaoke with her family. "I looked up to Whitney and Mariah and Celine endlessly," she says. "I think that's a large part of the reason why I learned to sing." She spoke with Tonya Mosley about auditioning for and landing the role of Glinda in Wicked, her signature whistle register, and how she quiets the voice of self-doubt.