ESRI StoryMap is an easy to use web building tool that allows for the integration of text, photos, videos, external online content, and maps (via ArcOnline) into a web page. They do not need to include a mapping component, in spite of the name.
In order to use the StoryMap apps, you need an ArcOnline account. You can make a public account here. If you are an MSU affiliate, it is suggested that you get an MSU organziation ArcOnline account by emailing firstname.lastname@example.org and requesting an account. An organizational paid licensed account will allow for the hosting of photos (with a public account photos need to be hosted via a service such as Flickr) and access to premium data layers when mapping.
StoryMaps are being shifted to a new version which is in beta testing. However, classic StoryMaps are expected to be available for some time to come. Relevant links for both types can be found below.
It will be possible to create classic version StoryMaps until July 2020. After July 2020, it will be possible to edit existing classic StoryMaps until July 2022. Classic StoryMaps will be sunsetted completely in July 2024. Stories will be able to be viewed post July 2024, but will not be editable and th apps will not be updated for current browsers, etc.
More information on the transition from classic StoryMaps to the current beta StoryMaps can be found here, "Moving to the new ArcGIS StoryMaps."
There are several different types of classic StoryMaps. Different classic StoryMaps will be good for displaying different types of information. If you are presenting a lot of text, StoryMap Journal or Cascade may work best. If locating and relating content spatially is more important than text, StoryMap tour may be most suitable.
If you want to build a classic StoryMap, start with this page: Tutorials, links to build, and links to a gallery of Classic StoryMap examples can be found here.
The new StoryMap app is in beta and is still having new features added to it. In its current form, it behaves most like StoryMap Journal or Cascade from the classic apps.
To build a new StoryMap: the new StoryMap application can be found here.
If you would like more detailed information about the new StoryMaps here are some resources:
A video on how to use the new StoryMap application "Meet the new ArcGIS StoryMaps"
This is a useful blog post on using the Survey 123 field collection app and StoryMaps in an educational context: "Ten tips for using Survey123 and Esri StoryMaps in your classroom"