How do they work together?

From Torg Adventure

Karen pulled on {FIRST_NAME}'s hand until he moved to lie on top of her between her legs. His cock fit right along the groove of her pussy lips. She wrapped her legs around him and said, "Let's see how these two pieces work together. I can't believe I'm going to pop my cherry for homework!" Then she kissed him, swiping her tongue past his lips. He opened his mouth, thrusting his tongue past her lips. Karen was a virgin, too!

Then he humped his hips up and down, pushing his shaft over Karen's clit. {FIRST_NAME} had read "Everything You Wanted to Know About Sex" and "The Joy of Sex" before he was thirteen, the first stolen, er, borrowed from the library and then secretly returned, and the second found while exploring his parents' bedroom. He had the book knowledge to please Karen, just no practical experiments. Karen groaned at the stimulation to her body.

He went through the stages in his head that he'd learned from The Joy of Sex. First, arousal. His cock slid easily through her slit, so she must be lubricated, and, therefore, aroused. The second stage is Plateau. For that, he knew he needed to be inside the woman's vagina. He couldn't wait. He was finally going to lose his virginity.