The Joy-Con grip accessory (model No. HAC-011) included with the Nintendo Switch bundle allows you to combine both Joy-Con into a traditional-style controller.
Additionally, a Joy-Con charging grip (model No. HAC-012) is available and is sold separately. The Joy-Con charging grip allows you to keep playing while you're charging your Joy-Con, so you don't have to miss a minute.
How to attach the Joy-Con controllers to the Joy-Con grip or Joy-Con charging grip
Make sure the Joy-Con are correctly oriented. To ensure the right and left Joy-Con are positioned properly with the Joy-Con grip or Joy-Con charging grip, align the "-"symbol on the left Joy-Con with the "-" symbol on the left side of the Joy-Con grip or Joy-Con charging grip. Then align the "+"symbol on the Joy-Con with the "+" symbol the right side of the Joy-Con grip or Joy-Con charging grip.
Attach the Joy-Con to the Joy-Con Grip or Joy-Con charging grip. Use the rail on the side of the Joy-Con Grip, and slide the Joy-Con from top to bottom, until you hear a click.
How to detach the Joy-Con controllers from the Joy-Con grip or Joy-Con charging grip
Press the release button at the back of the Joy-Con while sliding the Joy-Con from bottom to top.