You choose an area of dim light or darkness that you can see within range and that fits within a 20-foot cube. Each creature within the area must succeed on Strength saving throw or be restrained by shadows until the spell ends. A creature restrained by the shadows can use its action to make a Strength check against your spell save DC. On a success, it frees itself.
Until the spell ends, you can use an action on each of your turns to cause a tendril of shadow to reach out and grab a creature within 15 feet of the area. The creature must repeat the saving throw. On a failed save, the creature is pulled into the area and becomes restrained.
If the area becomes bathed in bright light, the spell has no effect until the bright light fades.