Unfortunately, we generally try out our new apps sitting at our desk, on the bus or subway, or in a waiting room. Not places one expects to get good GPS signals. In all likelihood, your phone is very capable of getting a great fix on your position when and where you need it--outdoors.
How many signals? Signals from at least 4 satellites is good. To determine a location on the surface of the Earth, 3 satellites is enough. The fourth helps your phone trilaterate your altitude which is why you may get a position on Earth before the phone knows your altitude.
More inaccuracy. If your signal bounced off a building and traveled further than expected to get to you, it can throw off the calculations. Being indoors increases the likelihood of getting one of these indirect signals.