By definition an artificial obstruction is anything on the golf course that is man-made in the way of your golf ball. This can be broken down nicely into two categories: movable obstructions and immovable obstructions.
A movable obstruction is a something small that you can, surprise, move out of the way. Things like empty “soda” cans, lawn rakes and trash would fall under this category. You’re allowed to move these types of obstructions out of the way or, if they’re making physical contact with your ball, you can mark where your golf ball is at before removing the object.
An immovable obstruction is then, obviously, something you can’t move out of the way of your golf ball. These types of objects are typically permanent features of the golf course like sprinklers, utility sheds or even stand for spectators. If your golf ball stops on, in or under an obstruction like this you are allowed to seek relief by moving it back into play without penalty.