What should i buy at the grocery store to stay healthy? which foods are superfoods?

No such thing: Claims that some particular item is a "superfood" is entertainment. They're lying to you. You don't see the NIH cafeteria offering "superfoods" and trust me, the research piranhas know the score. Avoid the very greasy, very sugary, and very salty stuff. Choose a good variety, don't overeat, and recognize that physical fitness is far more important in the long run than food choices.