The Incident Command System (ICS) "is a standardized approach to the command, control, and coordination of emergency response providing a common hierarchy within which responders from multiple agencies can be effective." (Wikipedia) The goal is that in any situation, anyone can step up and start managing it; as the response grows and multiple people from multiple agencies become involved, control is transferred & distributed gracefully as appropriate, with execution happening in a pragmatic way to keep things running smoothly, with clear communication and without "turf wars".
To be effective, everyone involved in an incident response needs to use the system. This implies that they need to know the system. Increasingly, agencies demanding that not only their employees, but any volunteers working with them be able to certify that they have received the appropriate training and can function adequately in the ICS environment.
Just as we encourage our members to organize/join CERT groups where possible, we ask that everyone take the basic ICS courses -- at the very least, the ICS-100. Some of them are available as free online Independent Study courses; others require in-person attendance at classes sponsored by the DEM and other groups. Recommended general classes:
ICS-100: Introduction to the Incident Command System
ICS-200: ICS for Single Resources and Initial Action Incidents
IS-700: National Incident Management System, An Introduction
IS-800: National Response Framework, An Introduction
ICS-300: Intermediate ICS for Expanding Incidents (in-person only)
ICS-400: Advanced ICS for Command and General Staff (in-person only)
You can take the 1st 4 of those at FEMA's Independent Study website. (See also the links on the individual courses above.) You don't need any credentials to study, but to be official and actually get a certificate you'll need to get a login.gov acct if you don't already have one. (Sorry!)