In order to add a new file, you can use the shortcut Ctrl-M.
If you mean how to use fstream, then you have to:
#include <fstream>
//after using namespace std; you have to put the next lines:
ifstream f("file.in");
ofstream g("file.out");///the name "file can be changed to whatever name you want, as long as you create files with the same names
//now you can use f exactly like you would use cin and g like cout
//note that instead of f you can put fin or whatever you like;
//the same goes for g