Attaching/Detaching Joy-Con with a Joy-Con Grip
By attaching the left and right Joy-Con controllers to a Joy-Con grip, you can play using them together as a two-handed controller.
*This also applies to the Joy-Con charging grip (sold separately), and attaching/detaching the controllers is done in the same way.
Attaching
Slide your Joy-Con controllers from above onto the left and right Joy-Con charging grip rails until you hear a click, making sure the orientation is correct.
Detaching
Holding the release button located on the back of the Joy-Con, slide the Joy-Con upwards.