The phrase is used to mean “How is this relevant to the conversation?”, especially if a person seems to be actively avoiding the topic being discussed.
Me: Hey, do you have that $20 bucks you owe me.
Him: Hey, have you seen the movie Hot Tub Time Machine yet?.
Me: What's that got to do with the price of cheese in China?
The ability girls and women have developed to hold several items at once in one hand. The skill has been developed due to the lack of pockets in women's clothing.
I thought she'd need multiple trips to carry her phone, keys, wallet, and Starbucks to her car since she needed the other hand to open the door, but she used her impressive girl grip to carry everything in one hand.