How to type text into GUI elements

this does nothing, but returns the region of the frontmost window
       App.focusedWindow();

so a possible usage:
       reg = App.focusedWindow();

       Pattern m_upload = new Pattern("D:\\Sikuli\\file.png");
       s.wait (m_upload, 3);

since you do not have any function before, that gives focus to the element, where you want to type, type will type to whatever GUI element has focus in the moment (apparently your IDE window)
      s.type("path");

I guess, this would be sufficient (having had a short look on the interesting webpage):

App.focus("Firefox");
reg = App.focusedWindow();
Pattern m_upload = new Pattern("D:\\Sikuli\\file.png");
reg.wait (m_upload, 3);
// give input focus to the entry field
reg.click(); // supposing a suitable click target
s.type("path");

Thank you for helping me..But still i cant get the result..

After clicking web element "d" its opening a file explore and i need choose file from there.
So i am giving a path in the "Filename" area and i need click on the "Open" button .
plzz help me.

driver.manage().window().maximize();
     WebElement d = driver.findElement(By.id("photo"));
       d.click();
       Thread.sleep(5000);

       Screen s = new Screen();
       App.focus("File Explorer");
       Region reg = Region(3,0,687,482);
       reg = App.focusedWindow();

       Pattern m_dropdown = new Pattern("D:\\Sikuli_Image\\file_name_path.png");
       reg.wait (m_dropdown, 3);
        s.type("C:\\Users\\vinumonp\\Desktop\\Bug");

sorry, but this are Sikuli basics and I do not have the time to write your code.

to be able to type anything to anywhere, you always have to take care, that the GUI element has focus (has an input cursor, ready to accept keyboard input).

To give focus to any GUI element, you have to do the same as manually:
click(the _correct_place); // usually inside the textfield
type("whatever");

or you might as well use the TAB key to jump from GUI element to GUI element if this is more suitable.