Yes the F/ number (So f/28. for example) is the aperture setting. It's how wide the opening is on the lens - and paradoxically, the smaller the number, the wider the opening (And the more light will be let into the camera).
Lets use an analogy here - say the camera is a tap on a bath. The shutter speed is how long you leave the tap on for - obviously, the longer it's left on for, the more water makes it into the bath. In this, how far you open the tap is the aperture - obviously opening the tap more allows more water through, so more water makes it in again. The game of photography in manual mode is balancing these two - so, if the shutter speed gets faster (Less time for the light to hit the sensor), you need to let more light in by widening the aperture.
So, if you want a faster shutter speed (1/30 of a second or higher is recommended to avoid camera shake - to freeze the movement of your subject, ideally you're looking for at least 1/50 of a second or faster), you have to open the lens up (Adjust so that the F number is SMALLER). It's complicated, but you get used to it quickly.
Aperture however also controls depth of field (This really complicates things, so only read on if you feel up to it) - how much of your photo is in focus. If you have a wide aperture (F/2.8, for example), your subject will be sharp, but basically everything else will be a blur - this is how you get those macro photographs with the beautifully smooth backgrounds (Called bokeh, incidentally). But if you have a high F/number (Small opening in the lens), then you get a greater depth of field, so lots of your photo will be in focus. This is great for landscapes, when you have a lot of light avaliable. This is why manual mode gives you so much creative control - you can change basically whatever you want about your photo.
ISO is a whole different ball game - It's basically for use only if even at the widest aperture you have, your shutter speed is too slow. Simply put, it makes the image sensor more sensitive to light (Each setting doubles the sensitivity of the sensor). So an ISO of 200 is twice as sensitive as an ISO of 100. This means that you need the shutter open for less time for the sensor to register an image. Sounds great doesn't it? But unfortunately there's a downside, particularly on compact cameras like yours. When the sensitivity is increased, the sensor gets interference from electrical signals produced inside it, resulting in 'Noise'. This is that unsightly coloured graininess you might find in some of your photos. It is the bane of photographers everywhere - although in modern DSLR's it very acceptable, in compacts with small sensors such as your Fuji, noise can be a massive problem at higher ISO's. So it's best to stick to the lowest number you can get ISO to. However it's better to get a noisy picture than no picture - so if you have no choice, boost it up and see what results you get.
