What is the use of setParam in Salesforce lightning Components?

in simple words, it provide value to parameter for example-
var show = $A.get(“e.c:testingApplicationEvent”);
show.setParams({“message”: “HeyBoy how are you “});
show.fire();
here message is an attribute , we set the value of attribute to “HeyBoy how are you ”
hope u understand i’am newbie?