To create a frame by frame sprite animation in Unity, follow these steps:

1. Select your sprite sheet asset in the Project View.
2. Unfold the sprite sheet to see the individual sprites (children objects of the sprite sheet asset).
3. Select one of the sprites, and then drag and drop it into the scene's Hierarchy.
4. You can rename the created game object.
5. With the game object selected, go to Window |Animation.
6. Click on the Create button in the Animation View to create a new Animation Clip.

7. Adjust the Samples to the number of frames per second your animation was created with (12 in this example), as shown in the following screenshot:

8. Make sure the record button is pressed. In the Project View, select all the frames (child sprites) in your sprite sheet asset and drag them into the Animation View.
9. A frame by frame sprite animation will be created. Click on the Play button in the Animation View or run the game to see the effect.