I've lost count of the number of times I've heard fledgling photographers ask "Do you just shoot in P, in auto mode? Can I get by with that?"
I shot in auto the first year of my business. It's true. Everything was going just fine... so I thought. Then I second shot for a man who told me otherwise (I wish I remembered his name, as I only shot with him that one time and I don't even remember who to thank for this lesson.) He took my nikon d70 out of my hands, put it on manual mode and said something like "Don't take it off. You're a professional now. Do you see that little light meter at the bottom on your image when you look through the viewfinder?? ... Well just ride that light meter. When that line falls close to center, that's when you take the picture, when it's evenly exposed. Move the shutter speed and aperture dials until it's center. Look at the back of your camera every now and then to confirm the shot is what you want."
Granted, I already had a foundation in knowing what aperture and shutter speed were, I just didn't know exactly how they related to giving me the photograph I wanted.
I learned. You'll learn. As with any hands-on hobby the more you do, the better you'll be. "Stop reading and start taking pictures." Those beautiful blogs you peruse for 5 hours a day will only get us so far. We must stop dreaming and start doing, be it even by mistake. Keep a journal, a small notebook every time you get a shot exactly the way you want and write down the shutter speed and aperture combo you used.
There is freedom in shooting in manual mode. You know you're past time to learn when you're not happy with the results that "p" is giving you. In other words, that shallow depth of field that makes one thing in focus and another out of focus- isn't that pretty? Well if you're in bright sun light, chances are auto won't let you get that shot.
What about trying to get a long line of people in focus? If you're in a dark or low light environment auto mode will open up your aperture so wide to collect as much light as possible and you might end up with one person in focus and one out of focus!
Never ever forget: knowledge is power.
We are all better by making mistakes. "A mistake means we stopped talking long enough to actually do something."