Those little metal dots are the sensors behind Core's tracking magic. Using surgical grade stainless steel sensors and the same technology that your hospital would use to check on your heart, Core is able to measure and track how meditation is affecting you.
As you meditate, try to keep your hands over the sensors. It should feel pretty natural to have your thumbs rest on them.
Don't worry about having your hands cover all the dots, just make sure you're touching a few on each side so that Core can get an accurate picture of your stress levels.