aine.. it should have a thumb hole at the back.... basically you have your thumb on for the low octave, and pinched (half covering the hole for the top octave).
Recorder fingering is different.. for a start you have an extra hole for the little finger of your right hand.... helping you to get middle C, and the thumb hole mentioned earlier.
recorders are chromatic.. you can play in any key whereas the whistle is more limited.
if you are after a more mellow sound I recommend trying a lower whistle... the Bb is lovely, and not much bigger than the D... but that depends on what key you want to sing in. They teah recorder in schools you should be able to find a tutorial in a music shop.