I'm not sure the XS can bracket.

fStop is basically the depth of focus. A low number, or high aperture, will open the lens up really wide allowing as much light as possible to enter. But the downside is it makes your focus depth very shallow making most things aside from the subject (or focus point) soft and out of focus. This photo is an example of such (Yes, I had to crop out the bottom half, sorry) You'll notice even her tattoo is "soft" and that is only a few inches from her face, the focus point.

With a high fStop number, or low aperture, you will have the lens open a very small amount not allowing much light in at all. But you will have a very large depth to your focus, like in the photo below. Notice not only the subject is focused but also the structure behind her, some 45 feet away from the focus point.

ISO (or ASA) is a reference back to the film days. The "speed of the film" or actually, the size of the Silver Nitrate particles on the film. Quick photo history lesson..... Silver Nitrate is what makes photography happen and it is sensitive to light. A 50 ISO speed film has very very small particles, whereas 3200 ISO has really big particles. The smaller the particle, the more light it needs to expose correctly, thus affecting the exposure time. The larger the particles, the more light is absorbed in a given period of time and as such needs less time to expose the shot correctly. The drawback of high ISO speed films is the grain that is created by the LARGE particles.
The reason behind why we still use the term ISO is because of the way the image sensor works.... When we make it more sensitive to the light, we also add more "noise" to the frame. So these days, we replace "grain" with "noise." For practical purposes it's the same exact thing.
I sent you a PM with my email.
Exposure is the only one I understand and can effectivly adjust. I'm still not sure what the F/stop and ISO speed do. I've expimented with them but can't figure out where to set them so I leave them on auto usually. I know about as much about photography as a two weeker knows about AH lol
I'll do some research on bracketing and see what I can learn from that!