What’s the difference between 넣다, 놓다, 두다, 꽂다, and 끼우다/끼다?

꽂다 typically means sticking something pointy into a tight space, whereas 끼다 gives the feeling of sliding/wriggling into the space.

놓다 emphasizes the physical action of letting go/leaving something, while 두다 emphasizes leaving the thing be.