Draggable slider showing before after

Hello - I am trying to create a draggable slider that shows before and after, similar to what @StevenWolpe has created in the link below. was wondering if anyone can point me in the right direction to get started?

Step 1. Create Empty Custom material
Step 2. Sample 2D texture > Camera Input
Step 3. Plug Sampled Color and (0,0,0,0) into Lerp
Step 4. create number variable that plugs into lerp function
Step 5. Plug lerp into material output
Step 6. in VS panel plug Set Material Number to Finger Touch X coordinate
Step 7. add custom material to custom post effect
Step 8. Remember to go into material render setting to change blend mode to Normal (to enable transparency).
Step 9. If you want an icon to move with the split, then place it in scene and use finger touch x coord to update the x position of slider bar icon.

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