What do these icons mean?

Hi There,

I am working on a website set up by someone else.  I am not super familiar with Squarespace.  Can you please tell me what theses icons mean and what the difference between them are? 

This is the left navigation menu in "Pages", by the way:

And how would I go about replicating these kind of sections? Thanks.

Thanks! Kinda got it now, and got the difference between index pages and folders.