If you dont know your way around then P mode on the Cam and full auto on the flash (ETTL) and leave the head at 90degrees pointing forwards. It then behaves just like a HUGEly powerful popup flash.
Past that its a learning game...
If you take the flash head and tilt it or rotate it then it will not auto zoom (to match the lens setting) you'll have to do that yourself, or change the flash compensation (cam or flash). It does largely depend on what you are pointing the flash at, how far away it is, how big the space you want to light and the colour/reflectiveness of the objects in the scene.
Note though that you'll need to pull out the built in diffuser if you are down at 17mm.
If you do this then make sure that it is properly clicked back in when you are finished otherwise the ETTL flash zoom doesnt (it stays at 17mm).