꽂다 is inserting something so it stays upright or lodged: a rice cake onto a skewer, a bookmark into a book, a pin into hair to hold it, a cone-shaped piece into a base, a nozzle plugged in to fumigate a house. Almost every line uses the adverb meaning like this, because someone is showing the motion as they speak. One line uses it figuratively for driving a bowling ball hard into the middle of the pins.