What is the first step to creating an informative essay?

The first step to writing any essay is brainstorming, but I don't know if your instructor wants that. I would just say it's either getting a hook, writing a thesis, or just plainly brainstorming.

You need to actually know the topic.

If you write something, pretending to know something, then you will not get anywhere. Teachers and academics alike will not like reading something that is not researched properly.

So know what you are writing about. That is the very first step.