How do I make that an object appears, like with some effect of de-fade, and how do I revert it?
This would be a simple way to do by adding a tween behavior to your object. You would then just need to substitute the conditions you want to use.
Remember to check if the other tween is still active, and remove it when you create a new tween. Otherwise there will be some weird behaviour.
So, if I want to use tween in another object, I have to delete the first tween I made? How?
So I want some text to appear and disappear with a certain amount of time between the “fades”, but I’ve tried using several actions and it won’t work
No, tweens are specific for the object they’re created on, the name is just an identifier. So you can have tweens named “fadeOut” on multiple objects, running at the same time with different values/settings.
But if you have a fadeOut tween running on an object and then create another fadeOut tween on the same obejct, or create fadeIn tween on the object that runs at the same time, then it can cause behaviour issues.