These records are used by mail servers to determine where to deliver emails. MX records should only map to A records (not CNAME records).
If an MX record is missing for the domain the mail for the domain will normally be attempted to be delivered to the matching A record. So for the domain “example.com” if there were no MX records for “example.com” then the mail would be attempted to deliver to the apex/root record of “example.com”.
Name: This is normally always left blank for MX records. This will be the host for your domain which is actually a computer within your domain. Your domain name is automatically appended to your name. So if you leave it blank it will be the instructions on where to send email for your domain (i.e. [email protected]).
Server: This will be the host (the mail server) that will accept mail for the host that is specified in the name field. Your domain name is automatically appended to your value if it does not end it a dot.
MX Level: The MX level determines the order (which mail server) that your mail will be attempted to be delivered. The mail server with the lowest MX level will first be attempted to have the email delivered.