what difficulty does everyone play at im new to this game

Honestly, I'm not super good at strategy games, and Heroes of Might & Magic III was my first turn-based strategy game ever two years ago. So I know that there are a lot of discussions on these forums about playing one or another campaign on "impossible" difficulty, and how playing at a lesser difficulty poses no challenge and serves no purpose, bla bla bla, where veterans who know the game perfectly discuss extremely minor changes in strategy to win ...

But if you're like me and are NOT a strategy gaming veteran (I was really more into RPGs and action-adventure games), you might want to try on the easiest difficulty (yes yes, the "easy" one) for starters, and gradually increase it when you learn to master the game.
For instance, now I never go below "normal" mode, as "easy" mode had actually become too uninteresting to me, as I know the game a little bit better. But I'll admit freely that I only go on hard/expert mode when I feel that I can handle it in the scenario in question, or when I'm playing a campaign and I'm two-three scenarios in and have some advantages (upgraded heroes, etc). I'm not sure I EVER played any scenario on "impossible", because starting without ANY ressources just sounds so scary to me XD

Then again, maybe you're good at turn-based strategy games, and after two-three games on "easy", you'll get bored and switch to higher difficulties. But I recommend starting with the lowest, just in case, so you don't get totally frustrated :)

There is a learning curve so until you know the strengths and weaknesses of castles/units and different spells, take your time and read descriptions. Campaigns are also good to familiarize yourself with this. In the end, it depends on how much time you are willing to invest in it. But eventually the only difference will be the amount of resources you start with, and even 0 resources should not be game breaking when playing against AI.
For now, since you are new to the game, don´t bother with difficulty and enjoy the game at easy setting...