For anyone wanting to dig into the ICS the authoritative introduction is the NIMS IS-100[1] course. Be aware that it's your standard government produced course, i.e. not entertaining in any way but generally manages to get the point across.

If I understand/remember correctly, IS-100 and 200 are the required courses on ICS (along with 700, 800 for NIMS itself) for all frontline firefighters on any fire department wanting to receive federal money.

1. https://training.fema.gov/is/courseoverview.aspx?code=IS-100...