Someone who's handy is skilled and clever, especially when it comes to making or fixing things. If you're handy in the kitchen, you're a good cook.
A carpenter tends to be handy with a saw or a hammer, and if you're good at sewing, you're handy with a needle and thread. Another meaning of handy is "useful" or "convenient." Your laptop is handy because you use it for all kinds of things, and your smartphone is handy because you always keep it in your pocket — it's right there when you need it.