I think the reason you’re not getting answers is that your question is extremely broad. Moreover, dozens, if not hundreds of topics on this forum have discussed these already.
I suggest reading about segmentation first: Image Segmentation — 3D Slicer documentation
This page has a list of extensions, including some that provide deep learning based automatic organ segmentation.
RTSS export works from the Data module. See details in the documentation, but also there are forum topics about this such as this one.
Try these out; we will be happy to answer specific questions afterwards.