What each DNS record does

DNS is a lookup table that turns a name into an answer. The record type says what kind of answer.

The ones you will actually use

A — points a name at an IPv4 address. www.example.com → 203.0.113.10. This is what points a domain at a website.

AAAA — the same thing for IPv6. Add it alongside the A record, not instead of it.

CNAME — points a name at another name, and follows wherever that one goes. Useful when the target's address may change. ⛔ A CNAME cannot sit on the bare domain (example.com) alongside other records — use an A record there.

MX — where email for this domain is delivered. Nothing to do with the website; changing your site's A record does not affect mail, and changing MX does not affect the site.

TXT — free text, read by other systems. Used for domain verification and for the SPF, DKIM and DMARC records that stop your email being treated as spam.

NS — which nameservers are authoritative for the domain. Changing these hands the whole zone to somebody else.

How long a change takes

Each record has a TTL — how long other systems may cache the old answer. A change is visible to anyone who has not looked recently within seconds, and to everyone else once their cache expires. Lower the TTL a day before a planned change and you cut the wait to minutes.