new to android understanding the use of OutputStreamWriter in web service calls

I have been going over the following tutorial and came across this code which I do not understand the purpose of:

              URLConnection conn = url.openConnection(); 
              conn.setDoOutput(true); 
              OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream()); 
              wr.write( data ); 
              wr.flush(); 

I don't know what is the purpose of the above code and where is it writing this data to...

From what I could gather, the documentation states that it converts character to bytes... but then it writes it to some where... not sure why this is.