Step 1: knit to the point where the decrease is desired.
Step 2: Stick the needle into the next two stitches.
Step 3: wrap the yarn around the needle you just stuck into the stitches.
Step 4: Pull the yarn through the two stitches.
Step 5: Drop the two stitches off of the needle.
Now you have one stitch where previously you had two. This same procedure can be used for the K3Tog. The P2Tog is the same, just hold the yarn in the front of the needles.
I decided to take the video off, because the lighting was terrible, and made it hard to see anything. I plan on redoing this video this weekend.
Links for this tutorial and others can be found on the left side of the blog.