firstly, try to read more about the webutil library.
second, find below a basic code snippet to do the job:

--this code to open uploading dialog box

    V_CLIENT_PATH := CLIENT_GET_FILE_NAME(DIRECTORY_NAME => NULL
                                 ,FILE_NAME    => NULL
                                 ,FILE_FILTER  => 'ALL FILES (*.*)|*.*'
                                 ,MESSAGE      => 'Open a file'
                                 ,DIALOG_TYPE  => NULL
                                 ,SELECT_FILE  => NULL);

    -- create directory on local machine at client server
    HOST ( 'cmd /c mkdir'||' "'|| 'C:tempapplication' || '"',NO_SCREEN); 

-- this code to show uploading progress to user
    V_SUCCESS := 
WEBUTIL_FILE_TRANSFER.CLIENT_TO_AS_WITH_PROGRESS
    (CLIENTFILE       => V_CLIENT_PATH
    ,SERVERFILE       => V_SERVER_PATH
    ,PROGRESSTITLE    => 'Uploading file in progress'
    ,PROGRESSSUBTITLE => 'Please wait'
   ,ASYNCHRONOUS     => FALSE
   ,CALLBACKTRIGGER  => NULL);

hope this may help 🙂