Is there any primitives in svg such that I can draw arrow head easily?
I couldn't find one in the document. The one that I found is that I
have to define marker. Is that the best way to do it?


That's one way, and may be the best depending what you want to do.

Otherwise, check out the star tool. It's actually a polygon tool, and
you can make a triangle with it.

My prefered method though, is to use the pen tool, and just draw the
shape I want, then use the node tool to move the nodes of the arrow
head how I want it.

Hope that helps,
Michael Moore
Don't forget you can make your arrow on a separate page and save to a folder and then import it and resize it as often as you'd like. I keep a folder of hands, arrows, text bubbles and more.
Daniel Culver