A modifier is an icon which, when selected, modifies the meaning of the next mouse action in the drawing area (snap to end, tangent to an arc, etc.). As an example, selecting the endpoint modifier while drawing near the end of a line will force the object you are drawing to be drawn at that endpoint.
The following is a list of Claris CAD modifiers and their keyboard equivalents. You can have these equivalents show up in the modifier's icon box by selecting Show keyboard shortcuts in modifier icons under the General panel in preferences. You do not need to use the command key to activate these.
Any Point or Dynamic (N)
End Point (E)
Center (C)
Intersection (I)
Invisible Intersection (J)
Point on (P)
Box Corner (B)
Percent Of (F)
Perpendicular (P)
Tangent (T)
Offset (O)