What do arrows in the margin of an event mean

Hi , I was wondering what do the green arrows in the margin of events mean?

Triggered events. They are only executed when the correct trigger occurs, e.g. mouse click, collision

Thanks

Also how do you set all instances of an object to be invisible?

Another important info, they are only triggered ONCE, when that condition is reached.

Regarding your second question, by using Object > Set invisible should work for all instances. If it's not, you could use a For Each Object > Set invisible.

Thanks bruno