Line of sight would allow your enemy ai to acquire it's target (your player). Pathfinding could be used to have ai move towards the player (which you could update occasionally to see if the player or any obstacles have moved). Then once the player and ai are within your specified fire distance have the ai shoot. You might look at the turret tutorial as well for the ai fire angles, spawning bullets, etc.
It's all about what you want. If there are no obstacles, or if you just want it simple, you could move towards player x,y. There are about 50m combinations you could use for what you want to do, it's personal preference.
In your case, I would pull up the "Ghost shooter tutorial" and save it as a new file. Then test different ideas using it as your base-code.