Learn to play the melody of this song with your right hand alone, then you can add chords with your left hand. B flat will be the black key to the left of B. You may want to play the melody an octave higher than it is written since the right and left hand both need the C key.
Use correct fingering (the numbers between the treble and bass staves) and you will have a smooth melody.
The rhythm you add will be a waltz since the song is in 3/4 time. Begin ver-r-ry slowly with a metronome speed of 60.
When you can play it well at that speed, then try it faster.