This mudra is often used for meditation and when doing pranayama breathing.
This technique involves folding/curling the index fingers of each hand so they touch the inner base of the thumbs. The other three fingers should remain relaxed but straight. The hands should be placed on the knees, palms facing downwards.
If you cannot or prefer not to fold the index finger all the way down to the inner base of the thumb, you can instead just touch the tip of the index finger with the thumb.