Here you need to select an archive to unpack.
Press "Browse" button, locate your archive, put the cursor to its name and press "Open". Also , instead of using "Browse", you may drag the archive icon and drop the icon to this dialog.
After you selected the archive name, press "Next" button at the bottom of dialog.
Note that WinRAR may attempt to guess an archive name and set a name of some existing archive from your Desktop when activating the dialog. If it is really the archive which you wanted to unpack, just press "Next", but if WinRAR guess was wrong, simply select an archive name which you want, as described above.