[wulf]

Arguably f/5.6 was a great choice for this photo. If you had used a wider aperture (smaller number, like f/2.8) the branches immediately round the bird would have been blurred and probably more distracting or, even worse, you might have got sharp branches and a soft bird.

If you want to get your head round how aperture affects a picture, the best way is to go out and do some testing. Find a subject like a long brick wall or picket fence that will make it easy to see what is sharp and what is blurry. Ideally use a tripod or find a stable place to sit your camera. Now, focusing on the same point, take a series of pictures stepping through the available apertures. In fact, since you are using a variable aperture lens, do the same series of shots at both ends of the range and somewhere in the middle.

Back home, when you can see the images in detail on your computer screen, work through and see how smaller apertures (bigger numbers) let you capture more of the scene in focus. That is the effect known as depth of field.

Wulf