I'm making a quest to retrieve a key which is in an already existing container in skyrim. So I made the new key. Then, in my new quest, I created an alias for the container I want the key to spawn in. Then I created an alias for the key itself, ticked ''in'' and selected my container alias. Then, at the objective I want the key to spawn, I set the target to the key alias.

I thought that the key would spawn in the container when the certain stage of the quest was activated. But the key is always there, even when the quest didn't start. So how do I make the key spawn in the container only when the certain stage is reached?

Your aliases fill / created as soon as the quest starts, I haven't been playing with CK lately but you could try placing the key at an Xmarker in a holding cell and then try moving it to your container at the quest stage you want.

I'm on my phone so coding isn't good, but set the key to spawn AT the container, then on the quest starting disable the key. On the stage you want it to be in the container, use Alias_Container.GetReference().AddItem(Alias_Key.GetReference()).

Obviously name your refs whatever you've called them. Hope that helps!

Also, ensure you tick the Allow Disabled box for your key alias.