four color system – How does Evade/Dodge/Block trigger?

I’m a bit confused on how it triggers. Can you always use these, or do you have to take an action beforehand to use these (and if so do they count vs. all enemies of the turn or only vs. 1), … ?

Rules system is: 4C (Four Color System): It is an OGL/public-domain successor to the old percentile Marvel RPG system (with enough changes to essentially be a 2nd edition).