Can somebody explain D&D in simple terms?

I feel like this has been asked before but I have specific questions. I am playing through Baldur’s Gate 3.

Are there reactions in real D&D, where a character can step in and do something not on their turn? I don’t understand what that really does exactly or if I should be careful with reaction points.

I don’t understand saving throws.

I don’t get cantrips, they are lesser, unlimited spells?

I am not understanding how to read character sheets and all the wisdom, persuasion, etc. The game has tutorials but doesn’t explain, what does Wisdom do? How do traits affect a wisdom roll? Like my character is a Barbarian, why does that matter?

One last thing, what determines the difficulty class? I need to roll higher than x number, how is that decided? Why do I get docked numbers if my stats aren’t high enough? Like -1 intelligence?

I have looked things up and it just isn’t clicking. I am hoping since this game is heavily based on D&D that someone can explain without knowing the game.

I understand some things from previous RPGs but this is a little odd. I don’t know how to keep up with my stats and remembering them for checks.