What does changing the Lasso frequency and width for the magnetic lasso do?
#1
The magnetic lasso draws by looking for a change in contrast between parts of the image. The width tells how far it will look away from where you let the cursor go. In other words, if you don't want to follow the shape closely, then use a higher number. But if the art has other areas of similar contrast more than this distance away, then it might get mixed up and select these.
The frequency is how close it drops those little anchors (what you would get by a click with the polygonal lasso.
I think there is also a setting on contrast or some other term for setting the tolerance between the selected/unselected areas.
#2