Photography

ISO

ISO measures the sensitivity of the image sensor,use lowest possible iso.
Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor sports event when you want to freeze the action in lower light) – however the cost is noisier shots
100 ISO is generally accepted as ‘normal’ and will give you lovely crisp shots (little noise/grain).
Use Higer iso if : in dark situation

shuter speed

measured in sec ... or fraction of it. any thing more than 1/60 will give shake effect if used without triod or image stabilization
also bulb mode

Aperture

larger aperture (f/22)(eg for landscape,macro photo) give larger depth of field (vision),smaller(f/4.5)(eg for portrait) give smaller dof g for blured background