you need to understand the
exposure triangle.
to get a picture exposed you need to use shutterspeed, aperture and ISO together.. to control the light.
too much you get white, not enough you get black.
there is a little "bar" when looking through the viewfinder, that looks like this.. I | I 0 I | I
and it indicates whether it is going to be underexposed or overexposed. as you adjust the settings you will notice the bar move.
"0" is when it is what the camera thinks is the correct exposure.
as above.. i'd suggest using Aperture priority or Shutterspeed priority. first (read the manual to see how)
ISo..
a low iso number neams the camera is less sensitive to light (say 100)
a high iso number means its more sensitive to light (say 800)