Does anyone know how to use the skybox picker in ZDoom?

I've started on this map in doom builder, and I came across the skybox picker. From the sounds of it, it seems like a neat object, but alas I cannot use it...

Anybody have an idea?

Skybox picker "assigns" different skyboxes to different sectors. First You need a skybox-build one an place a skybox viewpoint in it. Give it a tagnumber. Now locate the sector that You want to have that specific skybox visible as the sky-place a Skybox picker thing there, and look at the properties-in the Thing ID Sky insert the tag number of the skybox viewpoint You desire. Simple-a little trial and error will get You around this cool feature quickly.

awesome, she works, thank you :)