If hands are folded with both index fingers parallel, they will come closer and touch eventually?
The easy way to explai the first phenomenon is that at rest, your fingers - all of them - curl. Relax on your bed on your back. No matter what direction your hands face, they will curl inward as if loosely holding an egg. That's the anatominal position of the hands at rest, because the finger flexors are stronger than the extendors. So once you set the finfers up, you'll tire of keeping them extended, they'll start  to relax, and in doing so, will tough.

If I'm understanding the second example, that's because the flexor tendons for your fingers are actually in your forearm. Squeeze them and it shortens the tendons causing flexion.