Introducing ducklings! Please help, I am a novice!

[duckchix]

[/IMG]Good Morning! I am a novice duck owner and out of two duck eggs I hatched a duckling a little over 3 weeks ago. It has been amazing watching her explore and grow. I didn't want her to be the only duck so I purchased a 3 day old male duckling two days ago. The older duckling is so much bigger than the new baby so they are in different brooder set ups. My question is how do you properly introduce ducklings and when should I do this? Thank you so much!!!!