I just happened across a free class being taught at Coursera by George Everly, one of the authors of this guide - and it's called Psychological First Aid. (Full disclosure, Dr. Everly is personally known to me, has taught me and is a colleague.) Dr. Everly teaches at a few places, but one of them is the Johns Hopkins School of Public Health.
This guide is great, but it may be a lot for someone to read and understand. Even better are his courses - any of his courses. You can access them via Hopkins' website too, or via Coursera, and if you don't want a certification, it's free. This course is designed for people not already trained in mental health or trauma, and everyone should take this course. It's free - it could be life-changing. The worst that could happen is you never use the information, which means you have averted being anywhere near violence, war or disaster, lucky you - though you will have wasted some hours.
I, personally, believe it's important to know basic 1st Aid, and this means psychological 1st aid too. I heartily recommend learning about resilience and stress response and self-care and the urgent but basic things that anyone who learns can do to change people's lives, or save them. (and that last phrase is not hyperbole. Trauma is the root cause of many suicides and many physical ailments, even more lives that are not being lived to potential.) Look up the courses, read this 200-pg guide. Be ready, then hope you just wasted your time.