It is a fair question. For the friendliest explanation I have ever seen, I recommend the book "The Black Hole at the Center of Our Galaxy" by Fulvio Melia. He shows that in visible light, our own galaxy's central black hole is completely invisible. He then walks us through the various frequencies at which we may try to view it. In infrared, it is barely visible because of the massive stars circling so close to it. In x-rays, it is far easier, and in gamma it becomes fairly clear.
What makes a black hole really stand out is the plasma jets. A singularity is only visible when it devours a neighbor star. The matter spirals in and accelerates to spectacular speeds before disappearing over the event horizon that makes a black hole black. The catch is that this acceleration creates so much energy that the black hole may actually explode the matter in a predictable cycle. More often, though, it slips toward the poles of the black hole and takes the form of two intense jets of energy erupting from the top and bottom of the black hole. These jets are how we began identifying black holes decades ago.
Of course, now that we know where they are, we can also verify them by observing how they lasso the blue giants near them and force them to stay in a relatively tiny orbit with ease. This motion is what allows us to estimate how many stellar masses it contains. Since black holes usually surround themselves with thick clouds of gasses and sometimes stars, they tend to be impossible to "see", so this recent visualization is practically a miracle.
