Knitting with two sets of circular needles

I am trying to finish a hat and it calls to decrease with double pointed needles but i was having an impossible time finding size 15 double sided needles and a girl in a yarn shop said I could just use 2 sets of circulars, but I’m not exactly sure how and she was a little vague when explaining it. can anyone help?

Here’s a video for you. Scroll down to Small diameter knitting on two circular needles.

That should help a bit.

Here are 2 more sites that I used to learn 2 circ method.