A CNAME is merely the name of a subdomain.
This rightfully means providing aliasing to our domain's IP for the purpose of creating other hosts and thus faking the outside that you have www, mail, smtp, pop3, ftp and anything else but in reality, these are simply being pointed to one IP. www is greatly needed because the non-technical class of users will mostly start typing in with www and without CNAME on your DNS records, an access failure might be unavoidable.
A subdomain is a domain under an existing domain and most definitely it is under a different IP since it is the large organizations or multi-national enterprises (with offices on different regions or continents) needing this kind of setup.
MX record is a way of helping the outside world to where their mail servers or hosts will send the messages by querying your domain's DNS server. If you have already some familiarity with BIND, it is done this way with the head portion stripped.
IN NS PARK11.SECURESERVER.NET.
IN NS PARK12.SECURESERVER.NET.
satimis.com. IN A 220.127.116.11
satimis.com. IN MX 10 mail.satimis.com.
satimis.com. IN MX 20 mailstore1.secureserver.net.
www CNAME satimis.com.
mail CNAME satimis.com.
pop CNAME satimis.com.
smtp CNAME satimis.com.
ftp CNAME satimis.com.
whatever CNAME satimis.com.
IN means internet and A means address. NS is nameserver or the authoritative dns server repsonsible for providing the authoritative answer. An authoritative nameserver is the DNS that hosts your domain. Then all the rest of the nameservers that are caching only your information are then non-authoritative but can provide the outside world with answer or return your IP address if it has not expired on their cache yet or has not exceeded its TTL (Time To Live) value defined. MX is mail exchanger or your domain's mail server. the '10' or '0' and the '20' or '10' means the hierarchy. The one with the lowest number is your primary and the highest numbered is your secondary that is only responsible to hold on your incoming mails while your primary is not available or in trouble. The secondary doesn't contain or host your primary's mail accounts. All of thse are called DNS records. And these collected records is saved on to a text configuration file called the dns zone file. A zone is actually a domain with its defined subdomains, hosts and addresses.
This howto can give you needed DNS knowldege.