What happens when you merge 2 accounts?

I started playing PoE2 by logging in with my steam account. I have played PoE a very little bit, but never gotten into it. I saw that my email wasnt connected to this account so i went in and wanted to fix that.

I got the mail, opened the link and saw that another account was associated with my email. I must have created that account years ago, because i had forgotten it existed at all.

If or when i click merge what will happen?
The link doesnt explain much.

Will i have 2 accounts under the same mail, or will the 2 accounts be merged into one?

Best Regards Oliver