The Iceverse is a universe created by the user Ice Star, hence the name. It spans multiple story arcs and includes everything from one shots that need no context to multiple novellas (or novels) in a series that need to be read in order to be understood, forming complete story arcs. Sometimes there's also just one shots that share a common theme, like a ship that is canon to the 'verse and the development of it. Stories can be almost any genre.

The Iceverse does not include any canon past season five of FiM. It also doesn't take into account any other FiM related merchandise like the comics, tweets from the staff, and The Journal of the Two Sisters. The only exception would be parts of Princess Cadance's backstory and the first three Equestria Girls movies, and minor setting references from Season Six, such as Saddle Row and Saffron Masala. All other characters that don't have defined backstories in the show - like Luna, Sombra, Discord, and Celestia - are often given extensive backstories in the Iceverse, and there are other characters (many of them historical figures) with their own backstories, as well as a fair amount of OCs that are featured along canon characters.

Read the story description, first and foremost. There's always notes there or links for extra reads in the Author's Notes - sometimes there's even lore! If something is marked as a sequel to another story with no note in the description of it being standalone, then there is a story arc to follow.