If you're good at something, it means that you do it well. For example, my dad is really good at a number of things, like writing, playing games and sports, and cooking.
One question that always comes up about people being good at something is whether their ability is "natural" or not. It seems that the idea of natural ability is very popular, but this concept is being questioned more and more. When we really study people who are very good at doing something, we often find that they practice a lot. A lot! Maybe the ability to practice a lot is the most important thing, and this ability often comes from enjoying the activity.
You can use good at and bad at to describe your ability, or lack of ability, to do something. When you put a verb after at, the verb should be -ing. For example: my dad is good at playing pool. If the activity has a noun form, you can also just use that, for example: I'm not very good at chess.
So, what are you good at?
P.S. Obviously, this post is dedicated to Bill Coulton. One of the things he's really, really good at is being a great Dad!