It doesn't.
Inherently going 'backwards' from STL to a usable CAD file is a nightmare. Many softwares which do import STL just produce a STEP (or similar) with all the triangular faces from the STL - result a HUGE file that you can't realistically edit.
For simple stuff, I use the measurement tools in the free version of Netfab to get dimensions from STL. Real reverse engineering needs specialised tools.
There are a small number of applications which do a reasonable job of trying to convert STL to 'sensible' CAD geometry - at least one has been mentioned on the forum (name escapes me just at the moment).