How do I make a cut parallel to an edge? How do I make the cut in the picture parallel to the active edge? How do I also make sure the thickness of the cut of area is a certain value (in this case 3mm).
To get a precise value, you can use Bevel

Bevel the selected edge with 2 segments, Profile = 1
Adjust the thickness in milimeters
Delete &gt; Dissolve the unnecessary edge