Answer to Question 1
A stop occurs when a reasonable person would not believe that he or she is free to leave. A nonstop occurs when a reasonable person would believe that he or she is free to leave. A nonstop requires no justification at all because it is not considered a seizure within the meaning of the Fourth Amendment.
Answer to Question 2
When a suspect is handcuffed, placed in the back of a patrol car, and driven to the police station for booking, an arrest has occurred.
If a person is confronted by a single police officer and asked general questions about his or her suspected involvement in a crime, a stop has occurred.