Working into a stitch vs. a space

Hello: I am not sure why I am having so much trouble with the following round of my slouchy woodland hat but I am. It reads (2 dc in next dc, 2 dc in ch-1 sp). I am just not seeing the difference between working into the stitch and working into the space of next stitch I hope I am making sense here. Clarification would be much appreciated.

It’s the difference between placing the crochet hook between the strands of the chain and completely under the chain. Here’s a good video: