This article explains how to charge your Nintendo Switch Joy-Cons. Depending on the accessories you have, or if you want to keep playing while they charge, you have simple options.
Nintendo Switch Help – How to Charge Joy-Con Controllers! Joycon Charging Tips!
The easiest way to charge your Joy-Cons is to connect them to your Nintendo Switch. And you can use the dock or AC adapter that came with your gaming unit to charge your Switch and controllers. Slide your Joy-Cons into the sides until they click. Then use one of the following options.
The dock that comes with your Nintendo Switch gives you an easy way to keep everything charged. And it’s ideal for when you’re not playing a game to keep the unit plugged into this charger so it’s ready to go when you are.
Make sure the dock is connected to a power outlet via the AC adapter, your Joy-Cons are connected to the Switch, and then place the device into the dock.