3D support is still considered experimental and as such is not in the mainline release. To install the test build you will have to follow the instructions as laid out in the test thread [here] (which involves using the command line).
I think where you are getting confused is with the posts about people in the test thread having to downgrade to the 18.6 3D TEST BUILD from 18.7 mainline, which is different than the 18.6 mainline release which is what you would be currently on.