It is an ordinary server: we will run a web site on and it should be able to send/recieve email.
You should set up an A record, a PTR and an MX record, which points to the A record.
A: Mapping hostname to IP (server.foo.net -> 18.104.22.168)
To state the most obvious only, you will need an A record for the domain you wish to use pointing to that server, and you'll need to specify that server in the MX records of your domain. You will probably also want to setup SPF and SRV records as well, to help legitimize the standing of the email server.
Is there anything more specific you'd like some help with?