Demo account will be deleted after two months since your last login to the account. So in order to keep your demo account active you should login at least once in two months.
What is the difference between the demo and live?
trading with a practice account is technically the same as trading with a real account. The difference is basically psychological because virtual money is used. Trading conditions are exactly the same as on a real account.
What are the benefits of demo account?
If you are new to forex it will allow you to get acquainted with the trading platform and learn the basics of trading risk-free.