aspnetdb.mdf tables

 Hi,
 I would like to know more about aspnetdb.mdf database. Right now I have some doubts that I hope you could solve them. First of all, I have got a server where there are my own tables and there are, besides, the same tables that aspnetdb.mdf have. In fact, is like having 2 aspnetdb.mdf, one in my server and the other in App_Data folder. Is it like a security copy? When are these tables created? When I make a sql statement, where are datas saved? when I do a select, where is it doing select from?
 If you donÃ?´t understand the question, please feel free to ask me.
 Thank you. 
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