Use a ~ and add the number of your creation.
For example, one of my creations has the number 245963. If I want to post it here, I say ~"245963" (without the quotes).

Result:

@Vlad_Corvette
Go to that save and you will see in the address bar this: https://powdertoy.co.uk/Browse/View.html?ID=245963

You get that number from the ID=245963