How to adjust the depth of field?
Id like a more shallow DOF in my pictures, i have a nikon D90 and use the kit lens for now. I take portrait pictures of people so how can i (step by step) adjust to this? (i'm not to familiar with adjusting the setting on my new camera so i need steps if you know them)
1) 'A' Aperture Priority Mode.
-This will allow you to control how much DOF you want.
2) DOF in general, is resulted in the f-stop. Lower f-stops (like f/2.8) will give you a shallow depth of field, while high f-stops (like f/16) will give you deep depth of field.
3) The more you zoom in, the more "depth" you will get, so depending on what lens, stand a bit away (not too far), and zoom in.
There are only 3 factors that affect your Depth of Field (DOF):
1) The focal length of the lens.
2) The f-stop (aka aperture) used.
3) The subject distance.
DOF is that area in front of and behind your subject that is in acceptable focus. It can be very shallow: 
or very deep: 
or anywhere in between.
These sites will help you learn about DOF and how to control it:
http://www.dofmaster.com/dofjs.html
http://www.kamerasimulator.se/eng/?page_id=2
http://www.illustratedphotography.com/photography-tips/basic
At the 1st.site listed you'll find a handy DOF Calculator which you can use to compute your DOF for any combination of the 3 factors imaginable. To simplify things I suggest using a common subject distance of 5'-0'' and then check the DOF at 18mm at f3.5, 50mm at f5.0 and 105mm at f5.6.
NOTE: On a cropped sensor DSLR like your D90 a focal length of 50mm to 70mm is a good portrait focal length.
To help you get started I'll do 70mm at f5.6 with your subject at 5'-0''.
70mm @ f5.6 with a subject at 5'-0'' your DOF will be from 4'-10'' to 5'-2''. This means that anything from 0'-2'' in front of your subject (4'-10'' in front of your camera) to anything 0'-2'' behind your subject (5'-2'' in front of your camera) will be in acceptable focus. If you focused on your subject's eyes as you should then this shallow DOF may be too shallow since its possible that the end of your subject's nose could be out of focus as could their ears. You can check the DOF under the same scenario using f8 and f11.
I suggest learning to shoot in Aperture Priority since your goal is to control the DOF. Just watch the shutter speed the camera selects to be sure it isn't too slow if you aren't using flash.
Use a faster shutter speed, get close to the subject and focus manually or use the portrait setting if the camera has it. Using the faster shutter speed makes the lens open wider (lower f stop) and therefore a shallower DOF.