"Ought to" is used to advise or make recommendations. "Ought to" also expresses assumption or expectation as well as strong probability, often with the idea that something is deserved. "Ought not" (without "to") is used to advise against doing something, although Americans prefer the less formal forms "should not" or "had better not."
Examples:
You ought to stop smoking. (recommendation)
Jim ought to get the promotion. (It is expected because he deserves it.)
This stock ought to increase in value. (probability)
Mark ought not drink so much. {advice against something (notice there is no "to")}