Need to add a new option in leftnav as a slider


I need to add a new leftnav element which will be a slider as Jira Settings and on click opens the sub elements on transition, I need to know how that works exactly.
Like when we login, In the Navigator there is a option named jira settings which works as a slider and opens the sub elements like (System, Product, Apps). Just like this I am trying to add an option in my menu which will also work as a slider and on click transition to sub elements.
I want to know how the code for this slider works in atlassian-connect.json.

Thank You
Chirayu Bhatnagar