This is a great beginners page

http://www.pbase.com/wlhuber/the_basics

ISO determines how light sensitive the the camera is, if its day time and you want a long exposure you want a low ISO (80 maybe?) that way it doesnt matter that the shutter is letting a lot of light in, because the sensor is less sensitive.

Night exposures however you probably want to let as much light in as possible.

ALSO: long exposures need a tripod, or something to put the cam on, theyre impossible in your hands.

also worth noting, high isos may result in noise in your picture, but a program called neatimage (shareware) is very good for removing that!

Does your casio do shutter priority?  Mine (Z750) has a mode where you choose the shutter speed, and it sorts the aperture and all the rest to make sure you still get out reasonably exposed photos.  Might be a mode called "S".

ISO determines how light sensitive the the camera is, if its day time and you want a long exposure you want a low ISO (80 maybe?) that way it doesnt matter that the shutter is letting a lot of light in, because the sensor is less sensitive.

Night exposures however you probably want to let as much light in as possible.

ALSO: long exposures need a tripod, or something to put the cam on, theyre impossible in your hands.

also worth noting, high isos may result in noise in your picture, but a program called neatimage (shareware) is very good for removing that!

Ive managed 2 second exposures shake free, but it took like 15 shakey ones to get to that stage lol.

Thats right, although I aint sure why exactly, probably something to do with the distance from the lens to the sensor and stuff (am sure someone will come along soon and clear it all up)

But its why you see on lens specs a range of apetrure sizes, take my 18-55mm lens I got with my D50, it has a apeture range of f3.5-5.6.  Which means when the lense is at 18mm the apeture has a max size of 3.5 but when its at 55mm the max apeture is 5.6, it cant have a higher apeture than that value.

Going on a some specs of your camera your lens will do between f2.8-5.1.  So when your zoomed all the way out youll be able to have an apeture of 2.8 and all the way in youll be able to have an apeture of 5.1.

Cheers Brummie! That was great and very informative Problem with my camera is it only has two aperature values. 2.8 and 4.0 Ill just have to use the 2.8 for high shutter speeds and 4.0 for low

If thats the limit then some cameras can use neutral density filters that cut down the amount of light entering but without altering the colour balance so the end image looks the same but darker. These are often used by astronomers observing the sun with cameras.

For use without tripods take the focal length as the minimum shutter speed so a 500mm lens should get 1/500th of a second or use a tripod. For shorter lengths than 100mm I use 1/30th as a minimum to get a reasonable chance of shake free results.