There is a section in the command ref about array types. The problem with learning about arrays is that they are so simple - it's not the array itself that's the problem, its what goes around it.
An array is just a list. If you want to list each item individually you have to put them in square brackets like this [ ]
[loon1, loon2, loon3]
Sometimes a command or group of commands returns an array. For example
getPos loon1
A trigger automatically returns an array of the unit(s) that have fired the trigger. The array is called
thislist. So in the On Activation field of a trigger you could have
"_x setBehaviour {safe}" forEach units thislist
Hope that gets you started.