Of course, the anti-scratch lenses are made by coating regular plastic or glass lenses with a hard protective layer. In order to provide high-quality glasses, most online optical stores provide such kind of coating for customers.
Yes, because such coating can bring less prone to getting scrapes and ugly scratches on the surface of glasses, which can make your glasses more durable and less likely to break upon impact.
It depends on the store you choose. As I know, some online stores only provide original lenses that cannot prevent scratches. So when you buy glasses online, you should compare several of them and you’d better choose lenses with anti-scratching coating.