Dear Jenny:
hehe,It's a very "big" problem:)
Maybe it cannot be answered with few words,I advise you help yourself by using "SEARCH ENGINE",just like:
www.google.com or www.163.com,you can input Chinese“虚拟语气”,and you will get more information
about it.
I had tried it .The articles are all very good.Wish you can get more !
God bless you !