How to split column "In Progress" in Kanban board?

Hi, while doing following Module I've noticed on the screenshot below

That it is possible to split the "In Progress" Column into two different. 

I dig documentation, help community messages, stack exchanges but can not find the information on how to make it.

Does anybody know how to make it?

Thanks for your time and asssitance.

Best regards,

Stanislav.

#Trailhead Challenges