A very basic (but quite effective) method of estimating correct exposure in sunlight it the famous "Sunny 16 Rule". This states that for an average scene taken on a bright, sunny day, use f/16 at a shutter speed equivalent to one over the ISO setting; that is, f/16 at 1/100 sec (or the nearest equivalent 1/125) at ISO 100, f/16 at 1/200 (or the nearest equivalent 1/250) at ISO 200 etc. You can read more about this rule here:
Sunny 16 rule - Wikipedia, the free encyclopedia
However, most digital cameras these days come equipped with auto-exposure settings - the most you might need to do would be to bracket your exposures if the scene you are photographing has a lot of tonal variation.
The principle of shutter speed is pretty basic: the faster the shutter speed, the less light gets in. Fast shutter speeds are good for freezing action and cutting down the effects of camera-shake. Slow shutter speeds are good for low-light situations and creating those arty shots of blurred moving water.
As for macro photography, you just need to get as close as you need to get a good shot - it really depends on what you're shooting. The basic composition principle of "fill the frame" applies as much to macro photography as to any other field.
Hope this helps.