Index within a page

Site URL: https://hairdiagnostics.com/medical-conditions/

The website I've linked is my present website - not squarespace made. I'm a newbie and I'm redesigning that original site. I'm trying to replicate one of the features and struggling to see how on squarespace.

On the page linked there is an alphabetical index of medical conditions on the right so you can quickly jump to different conditions. It stays fixed as you go down the page.

Is this, or something similar, possible on squarespace?

Use an Archive Block. You can create an organized list of links to blog posts, gallery images, products, or events. You can choose to group links by date, category, tag, or author . The tag can be one letter A,B,C etc. It can be a list, or drop down. 

Thank you Derrick. Much appreciated.