I'm sorry if there's a super obvious answer, but I can't find it anywhere.
How do I get the things I build in custom structures creator into my custom scenario?
After I finish making them, I have no idea what to do from there. I clicked the save button when exiting the creator, but I can't find any trace of it anywhere. I've checked all of my documents files. 
I'm extremely confused. 

Hi Molly

You have to save your buildings using this button:



And selecting the area under the building you want to save.

Otherwise you'll only save the whole park with the structure in it but not the single structure to be re-usable.

Yeah, that will do it!

Thank you so much!

Glad to help you