How does an MX record go?

[Das Goravani]

I have switched where my DNS is done for my websites.

It was with GoDaddy, but I switched their name servers to routing to Cloudflare, today.

I believe I now have to setup an MX record for each site that I want mail for, on Cloudflare, they have the ability for you to do that.

When you are setting up an MX record it has these fields.. my question is WHAT GOES INTO THE FIELDS?

The have TYPE and that is MX
Then they have NAME and it says "Use @ for root".
Then they have MAIL SERVER and that is a text field but I don’t know what goes there.

Then they have TTL and that is on Auto
Then they have priority, and that is blank, numbers are what it offers to go in there, 1,2,3, etc. 

Mainly want to know what I put in MAIL SERVER.. I tried putting the domain name there, it didn’t seem to like that, I put the IP address, couldn’t tell if it liked that.. 

Do you know what I am supposed to put there?

Thanks

Das Goravani