Welcome to the community. The first step I would recommend is the Tutorials. The first one on the ghost shooter game (beginners tutorial) will cover getting an object to move towards the player. It uses the bullet behavior which is exactly what you want to do with your enemies bullets. In that example the player shoots toward wherever the mouse is pointed. Combining those pieces will give you everything you need to be able to have enemies shoot at you. also, you may want to look at the turret behavior as it has some nice automated ways of setting this up as well.
On a side note, as these are covered in the beginners tutorials and the manual very well, I would recommend doing them as you will get better responses to your questions when it appears you have at least put in some effort to finding the answer before asking on the forums. Not trying to discourage you, but folks respond better when you ask questions that are not answered in the beginners tutorials and manual. It ends up coming across as lazy.