Everyone knows this song, but some people as they get older tend to forget the lyrics exactly.  So here they are as a reference point.

If you’re happy and you know it
Clap your hands
If you’re happy and you know it Clap your hands
If you’re happy and you know it
And you really want to show it
If you’re happy and you know it
Clap your hands

Continue in a similar manner
If you’re happy and you know it
Stomp your feet.
If you’re happy and you know it
Shout “Hooray!”
If you’re happy and you know it
Do all three