If you are using the OpenFileDialog in Multiselect mode, it will return a property named FileNames with the full paths to all files. You can simply use a loop to iterate through the array:
foreach (string filename in openFileDialog1.FileNames)
{
using (FileStream fs = new FileStream(filename, FileMode.OpenOrCreate, FileAccess.Read)
{
// Here you do whatever you want with the Stream fs
}
}
Note: You didn't specify what you wanted to do with the file other than saying "store". If by "store" you mean making a copy of the file, the it is not necessary to open a FileStream (although you can if you wish); it is much simpler to just call File.Copy.