It's very easy to learn, you just have to try it!
As you are going around a corner, begin to push forward slightly on your inside handle (in essence you are "turning" out of the corner). This will cause the bike to lean in more and you will turn tighter. The reverse action, pulling on your inside handle, will have the opposite effect and will begin to upright the bike and you will turn less sharp.
It's easy - just do it slowly and you will instantly feel the effect. You have to trust that it'll work.
You can even do it going straight down the road. Just push on your right handlebar, and your bike will begin to veer off to the right side of the lane, then push on the left side and it will come back. This is a safe, fast, and accurate way to change lanes. It's quicker than just "leaning over" and having the bike drift into the next lane.
