Could you explain the story? I don't really get it

5185051
Each part is a piece of text that describes myth, maybe true or false, behind Equestria's known powerful figures, or at least texts that look like they're important.

The first is a letter written by Celestia about a time long ago. The second is an old story about the creation of discord.

5187929 I get that part. I mean I don't get the second story about Discord's creation. What happened to him?

5187941
By misusing kindness he brought discord and the first winter.

To punish him the other elements marked him forever by sewing the animals he once loved onto him. Then they sent him away to die for a while, at least until a new era came.

How transition between gens, like gen 1 - 3 isn't clear yet, but hopefully the rebirth of 'Sundance' will she'd a bit of light.

5188037 ...That's an awful punishment.

5188155
Mercy comes from kindness. There was none here, he lost that gift.