Well it was always available on
MSDN[
^]. Didn't you look on MSDN to find an answer to the problem?
Look into the documentation and check how can you get the user to be able to get a file selected from the File System using the OpenFileDialog.
Example code for this would like as below,
OpenFileDialog fileOpener = new OpenFileDialog();
fileOpener.MultiSelect = false;
bool? result = openFileDialog1.ShowDialog();
if(result == true) {
}