Not just you. Virtually everybody. There are only a handful of FREDders using it which is a real shame because it's hugely powerful.
I was going to point you at my FAQ but then I realised I haven't uploaded the changes that include an explaination cause I'm still tinkering with that page so I'll just post it here.
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When-Argument / Every-Time-Argument Probably the two most confusing of the new SEXPs for most people these two SEXPs are also amongst the most powerful. Both SEXPs allow you to do things that previously would have required a lot of tiresome fiddling with variables. In addition they also allow you to do things in 1 event that previously could have required hundreds.
You use these SEXPs like this. Suppose I had a senario where I wanted something to happen if ever Alpha 1 got within 2000m of any of Cancer, Leo or Libra wings. What you could do is make an event like the one to the left for each wing. Then in a fourth event I'd check if any of the events had come true and then do whatever I wanted to happen. That works reasonably well but what if there were 9 wings instead of three? I'd need ten events in total. Nine events checking to see if Alpha was close and one with an an enormous or SEXP checking if any of those events had occured. As you can see this would take a long time to make, uses up a large number of the SEXPs you're allowed in a mission and would be a pain in the neck to change if you wanted to add something to when the 9 events trigger (suppose you later decide that it only matters where Alpha is after a certain capship arrives. You've now got to go back an edit all nine events).
When-Argument gives you a way to do this more simply. The SEXP allows you to declare a list of ships that the rest of the event will apply to. The event to the right replaces the four events I needed to check the distance from Leo, Cancer and Libra wings with a single event. If I wanted to do the same thing for nine enemy wings I wouldn't need any more events. I'd just add the names of the six extra wings below Libra.
The event works quite simply. When the mission is running FS2 looks at the list of ships this event applies to. Whereever it sees the word argument it sticks in the name of the wing at the top of the list. If condition is true (i.e Alpha 1 is less than 2000m of Cancer wing) then the event triggers and whatever you've replaced do-nothing with will happen. If not FS2 goes back this time substituting the second name on the list wherever it sees argument. FS2 continues down the list until it reaches the end or finds something that triggers the event.
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It's not complete yet cause I need to explain the conditions that can trigger it and also show that it doesn't have to be ships in the list (It can be anything, Names of messages, Names of subsystems, Pretty much anything that can appear in a SEXP).
