The two magizines are very famous. What's different between them?
There is no magazine named "Science American" as far as I know. I think you mean "Scientific American."
"Science" is a professional journal which publishes original research papers in a variety of fields: biology, chemistry, astrophysics, physics... It also has news articles on science or topics related to science. It's published by the American Association for the Advancement of Science, a professional organization of scientists, for its members. The AAAS also holds an big annual conference where scientists present papers.
"Scientific American" is a popular-level magazine with articles written for the educated layman and professionals who like to read about what's happening in other scientific fields besides their own. It is a commercial (for profit) publication.
What's the difference between Scientific American and American Scientist then?
Scientific American is more widely-distributed than American Scientist, and has a more varied audience. American Scientist is published by Sigma Xi, the scientific honors society. Neither of them are peer-reviewed journals.
And I think "Science" is peer-reviewed, unlike the other two magazines.
Separate names with a comma.