The thing is finding the terminology, in the case of Redshift that is Sort Key, Distribution Key and primary key (though these aren't true primary keys they do influence the query planner).

It took me a few minutes but I found indexes are called projections in Vertica and are more like materialized views than true indexes, here are the docs with a breakdown, https://www.vertica.com/docs/9.2.x/HTML/Content/Authoring/Ad...

And here is a general walk through of the architecture including key concepts such as projections. https://www.vertica.com/docs/10.0.x/HTML/Content/Authoring/C...

In a few cases I have had to go to published white papers on the technologies as well.

But honestly it's all searching for the right words and then crawling through docs and papers.