Since you are new to Rhino here’s some further details:
WIP means Rhino 7 Work-In-Progress. It is not a ready-to-work release version like Rhino 6 is, but rather a current version of the Rhino 7 development work good for about 45 days after it’s made available. Usually a new version is made available every Tuesday, but not always.
If you are using the Rhino 6 evaluation the WIP is not available to you; it’s only for users who purchased a Rhino 6 license.
Rhino 6 has some very limited SubD features. The real SubD capability is in the WIP and is under active development. I’ve not seriously attempted to use it but those who have and reported their findings here seem to be full of confidence that it will be the greatest thing since sliced bread. However their reports usually contain some combination of lists of shortcomings and bugs and lists of features that are “essential for easy practical use” of SubD as a modeling tool - features that are common in other SubD modelers but “need to be improved” in one way or another.
If what’s there now will work for you then you will be ahead of the curve when Rhino 7 is released because you will have learned the SubD features as they are being developed while learning all the other features of Rhino.