Increases

From BluWiki

To do an increase you will basically be knitting into the same stitch twice.

You start by going into the stitch as if to knit

Wrap the yarn and pull through as if to knit, but don't take the old loop off the needle.

Enter the stitch again as if to purl.

Wrap the yarn as if to knit.

And pull through as if to knit. You will have two loops coming out of one stitch.

Now you can pop the old loop off the needle.

The video showing you how to do this is here.