To show TIG filler wire feeding there are two movies provided.
They show two / three stages
Close-up with gloves off. In the first three images of the "forward" feeding motion, the thumb is a soft guide upon the wire. For the fourth "return" picture, the thumb tightly squeezes and clamps the wire.
Beginning of forward feed motion with fingers
Middle of forward feeding action
End of forward feed with fingers extended
The "return" sweep of the fingers (exaggerated finger release from wire - in reality you would slide the fingers back along the wire). Thumb gripping wire.
Same visual content with more explanation.