Choosing manual vs. auto is actually simple. How much thought do you intend to put into your image-making? If little to none, then auto is just fine, as it will take care of all the pesky little details for you, and give you the best picture possible (which is to say, kinda OK). If you actually want to determine the outcome, having the image be more than a record of time and place, then learning about image-making (composition, light control, staging) and the technical elements of your camera will give you much better images, that will be interesting to people outside your immediate circle of family/friends.
As in most things in life, you get out what you put in.
Check out my sig - those words were written by The-Traveller, who in essence wrote a photography degree in three simple sentences.