Arrow[Line[...]] is equivalent to Arrow[...]. Arrow[Tube[...]] yields a 3D arrow based on a tube.
Arrow[{pt1, pt2, ...}] represents an arrow whose shaft passes through the sequence of points pti.
The positions of points can be specified either in ordinary coordinates as {x, y}, or in scaled coordinates as Scaled[{x, y}], or using ImageScaled or Offset. »
The shaft of the arrow consists of a sequence of straight segments joining the specified points.
Arrow[{pt1, pt2}] is drawn by default with its tail at pt1 and its head at pt2.
The form, orientation and position of arrowheads can be specified by an Arrowheads directive. »
Graphics directives such as RGBColor or Thickness apply to both the shaft and arrowhead elements of an arrow. »
You can prevent directives from applying to an arrowhead by including explicit directives within the graphic used to specify the arrowhead.
In Arrow[{pt1, pt2}, s] the setback distance s is measured in the ordinary coordinate system of the whole graphic, so that the arrow will just touch Disk[pti, s]. »
If the whole graphic does not have AspectRatio->Automatic, then a specified arrow setback may correspond to different distances in different directions in the graphic.
EXAMPLES
Basic Examples 
Scope 