6. The Tools in the Toolbox / 6.2 Tools for All Kind of Layers
Using the Vector Lasso you can create the lasso using curves and lines - similar to a vector layer.
The handling corresponds to the Curve Creation tool (see chapter 6.2.15). By clicking and dragging new curve points are created, simple clicking creates line points. Because you can't create a line point directly after a curve point, you can force to create one by holding Shift.
By holding Ctrl (Windows) or Command (macOS) a subpath will be created.