In every one of the 15 steps one is supposed (according to Halacha) to either do something, eat something or say something.
- Kadesh - one must do Kiddush - Biblical/Rabbinic.
- Urchatz - one must wash his hands - Rabbinic
- Karpas - dip vegetableinto salt water - (old standing) custom.
etc. However, what exactly is the Halachic requirements involved in Nirtzah. All the more so, where in the Hagadda of the Baal HaTanya, the only thing that comes after the fourth cup is Leshana Habaah.
What exactly is Nirtzah then?