How do you get reputation points if you can't comment or interact with things till you have reputation points but you need reputation points to be able to comment and to get the point you ..... went cross eyed.
You get reputation points for asking a good question and for giving good answers. This you can do immediately after creating an account. Once you've done some contributions you gain the privilege of commenting.
If anyone could comment just by opening an account, we would be flooded with spam.