Custom mx records

i’m moving a domain to dreamhost from another host. i want to use another mail server. what is the exact syntax i need to use in the custom mx record input field in the DH control panel so mail will be directed to it appropriately? do i just put the server’s ip address?
or do i need to input additional information in that field (i.e. preference)?
field> 10
can i even use an ip? do i need to use the dot at the end of the ip? the example in the panel just has “10

also, does this require unique ip for the site?