There are a few ways to use loops.
For one, you can use the action "For each integer A, do acvtions". If you set the number to something like "For each integer from 1 to 10", it will run through that action ten times. As an example, in about a split second, I can gradually set an integer variable to 10. YOu would do this like so:
"For each integer between 1 and 10, dfo actions
Loop actions
Set Integer = (Integer A) + 1"
thaqt will set that integer to whatever the loop's number is on plus 1. So if the loops has only ran one time, it would do "set integer = 2 + 1".
Kinda confusing, but it's helpful in more advance triggers.
There's also another type of loop, by contuinally running a trigger. That's accomplish with the "Run (This trigger) ignoring conditions". This will continually run the trigger over and over again, until you stop that action or remove it.
There's also another type of loop that's not ver good. An example would be whenever a unit enters a certain region, you'd move it to another region. And whenever a unit would enter that region, it would move it back to the other region. That would cause an infite looop moving the unit back and forth back and foerth, crashing the game.