After tooth extraction, should there be some puss coming out?

Not normal. If after tooth extraction there is a discharge of mucus, pus or blood you should visit your surgeon for post-op examination and treatment.
Two possibilites. If you are having the tooth removed because of an acute infection with swelling, i.e., an abscess, one of the goals is to establish drainage either by removal of the tooth and allowing drainage from the extraction site or by an incision adjacent to to the tooth. The other possibility is that following the removal of the tooth, a postoperative infection developed with pus draining from the site.