The Flu typically lasts from 7 to 10 days but in some cases the flu can last up to 2 weeks.
If the flu hasn't gone away by 2 weeks then you need to see a doctor because you could have some other virus.
When you have the flu make sure you get plenty of rest, drink plenty of fluids to stay hydrated and take cold and flu medicine and in a week or 10 days you should be feeling better.