There’s not much more you need to know. Try not to make the sign of the cross too often and enjoy your meal.
Since you are invited, I’m assuming at least part of the haggada will be read in English.
When you get to the part where the rabbis are discussing how many plauges befell the Egyptians, you will be reading a portion that is meant to show you, in a simplified way, how Talmud works.
You also may notice that the main human character of Exodus – Moses – is only mentioned once in the entire seder – perhaps to emphasize that it was God, not Moses, who redeemed our people. This may be the same reason as to why we don’t know were Moses was buried. So that people did not turn his grave into a place of worship.
Other things to discuss: Why did God harden Pharoah’s heart, and why does this not occur until the fifth plauge.
Now you can do a little homeword and wow your hosts at the meal