Help! Simple IRA through Work, But What Is It?

I was informed I am eligible for a Simple IRA through my employer, but I'm honestly clueless about all of this. They use Morgan Stanley, but I was just told that I need to open an account "somewhere".

I understand the whole percentage and matching part, what I don't understand is HOW do I open an account, WHAT info I need/my employer needs if I go with someone other than Morgan Stanley, and WHAT I do once I have money in the IRA account.

NOTE: I HAVE TO TURN IN THE PAPERWORK BY JANUARY 10, 2025!