Thank you, Soup for your correction. And much thank to David L.
Actually, I met the usage of this tense some times before and I also thought like David. My teacher shortly explained me as Soup did, but I still unease about this case.
It just like the matter was happening and suddenly, we appeared in a while and then, disappeared. And it means that we want to use this tense everytime we want to be there, and any one will accept the case, right?
I think David, me and more other people have the same query in here, so please help me make this issue clear.
I know I certainly meet this case in near future, and I really hope to be sure that I am cleared it by you all.
Thank you so much