Its an online resource I think, can't remember the URL, try googling it.
However, bear in mind that a lot of explanations are not accurate. I am personally not a big fan and will advise you to take caution or stay away from it altogether
Altogether I think It is a good practice material...Only problem is you can not find exact explanations and many times you have to assume the answers..Best thing is to go through Manhattan SC book and try to solve problems from SC 1000 and try correlating it which will give you a good insight of all the grammar concepts.
SC1000 is awful. it contains some good problems, but those problems are only good because they have been stolen from og10/og11/gmat prep. almost 100% of the problems that originate from SC1000 itself have VERY serious issues.
you have been warned. (incidentally, this is why SC1000 is a banned source on this forum -- because it's so bad.)