Ok Leo, let me see what I can do to help...
First off, your lens has a great range of reach, and the zoom is very versatile, so no problem there.
Av setting will set the "aperture value" hence the acronym "AV' on the dial. In laymen's terms, what this means, is the amount of light that the camera receives via the lens. This is known as an "f-stop" in it's most simplest form, if you turn the dial to Av, you then have control over the Aperture value, as well as ISO and exposure compensation. When on "Av" setting, and you turn the other control dial near the shutter button, you are controlling the cameras ability to absorb light. You will see the number change from 4.5 at it's lowest (I think, as this is based on your lens) to right up to 22.0. There is a direct correlation to this setting, and the speed at which your camera exposes (opens the shutter up, and takes a picture) At a figure of 4.5, your shutter will be open for a vastly shorter period than at 16.0 or 22.0 for example. So if you want a faster picture, delivering a sharper image, you want to go as close to 4.5 as you can.... I hope you are still with me... Also, the Av setting will allow you to control your "depth of field" This means that the same subject, at the same distance, with different Av setting will produce a remarkably different result, especially if you are very close to your subject. With a low Av value, such as 4.5, your foreground and background will be blurred, and you will have a faster shutter speed. With f16.0 for example, your depth of field will be deeper, and a lot more of your foreground and background will be in focus, but due to the increased shutter time, you will need that beanbag, as the camera takes a lot longer to open the shutter (this relates to your dawn and dusk question earlier), read and interpret the signal, before closing the shutter, and ultimately producing a photo. This time lapse is simply not possible when you hold your camera by hand, and needs a solid, completely immobile support.
There was mention made of ISO. If you are at f8.0 while in Av mode, and your ISO setting (this is a metering or scale of light) is at 100 you will see a certain number through your viewfinder which will be 1/xxx the "xxx" is the speed of the shutter. So let's say for example, because the numbers all depend on the available light, that you are seeing 1/60 while shooting on Av at f8.0 and having an ISO setting of 100. You are controlling the depth of field via your Av setting set at f8.0 and have an ISO setting of 100, but you are only achieving a shutter speed of 1/60 (this is desperately slow) You have two options to increase the shutter speed and get a sharper image. One is to change the Av value to a lower figure, such a 5.6, or increase the ISO setting to 400. Both will increase the shutter speed, but they will yield very different results. I do not want to bombard you with a whole bunch of jargon, so I suggest you find the time now, to play with the Av setting, as well as ISO. Take pictures, download them, view them and understand them as far as the changes in ISO and aperture go, and then I will give you a bit more info.
In a nutshell, and something to be aware of while you are playing. Higher ISO number means shutter speed which means a sharper photo. The lower the Av value, the faster the shutter speed will be, but the shallower the depth of field, so if you wish to take a landscape type shot, you would opt for a setting along the lines of f16.0 to f22.0 but you will HAVE to use a beanbag, as the shutter speed will be dismal. At f4.5, in dual and dawn light, the shutter speed may not be much different to f16.0 in midday light. This is because f16 is a pin hole of an aperture, but in midday, the light is bright, so the camera absorbs a lot of that and transfers it through the lens to the body. In afternoon dusk light, you will need that aperture wide open (f4.5) to absorb the same amount of light to generate the same shutter speed....
Are you lost, or has the above made sense? The best way to learn is to fiddle, but understand while fiddling. If you are still completely lost, send me a PM and I will be happy to call you.