Running iCall

Hi there, I'm a newbie trying to understand the powers of iCall. I have a very basic question which i can't seem to find a clear answer on which is: once you create your iCall script and Handler, how do you execute or make the F5 run the script? Does this occur as soon as you complete the Handler (i.e. after creating the handler it waits for the defined event to occur and once it does it starts running the script)?

thanks!