Nameservers vs DNS records: what's the difference?

Nameservers decide which company keeps your domain's settings. DNS records are the settings themselves: where the website is, where the email goes. Change a record when you want to move one thing, like your website, and keep everything else where it is. Change the nameservers only when you want a different company to take over the whole set, and only after you have copied every record across.

An analogy that holds up

Imagine your business keeps a folder of instructions for deliveries: which door the mail goes to, which entrance customers use, who to call for the stockroom. The folder sits in one office, and anyone who needs an instruction asks that office.

Changing a DNS record is crossing out one line in the folder and writing a new one. The folder stays in the same office; everything else in it is untouched.
Changing nameservers is telling everyone, "from now on, ask a different office". The new office has its own folder. If nobody copied the old instructions into it, they are simply not there.

That second point is the whole reason this matters. When a nameserver change goes wrong, it is almost always because the new company's folder was missing the email instructions.

How to see your current nameservers

Look up your domain on ICANN's lookup tool and find the "Nameservers" section. You will see two or more names, such as:

"ns53.domaincontrol.com": GoDaddy's DNS
"dns1.registrar-servers.com": Namecheap's DNS
"ada.ns.cloudflare.com": Cloudflare
"ns1.wixdns.net": Wix
"ns1.yourhostingcompany.com": your hosting company

Whichever company those names belong to is where your records live today, and where you log in to change them. Nameservers themselves are set at your registrar, the company you pay for the domain.

When to change only a record

For most owners, most of the time, changing records is the safer choice. Choose it when:

You are switching to a new website and keeping your email as it is. You change the website records (usually the one for the bare domain and the one for "www") and nothing else.
You are adding something new, like a booking page on "book.yourbusiness.com" or a Google verification code. You add one record.
You are changing email providers but not your website. You replace the MX records and the email trust records, and leave the website ones.
Your email is critical and you would rather not risk anything. Record changes touch only what you touch.

The step-by-step version is in connecting your domain to a new website.

When changing nameservers makes sense

There are good reasons to move the whole set:

The new provider requires it. Some services, Cloudflare for example, work by becoming your DNS company. Some website builders offer nameservers as their "easy" connection method.
Your current DNS company is going away. If your records sit in an old web designer's hosting account, or a host you are about to cancel, they need a new home before that account closes. Cancel the hosting first and your website and email go dark together.
You want everything in one place you control, with one login, instead of the registrar in one company and the DNS in another.
The current DNS screen cannot do what you need, such as a record type it does not support.

How to change nameservers without losing email

If you do move nameservers, the order is everything.

List every record at the current DNS company. Screenshot the whole table, or use an export option if there is one. Pay most attention to MX records, TXT records starting "v=spf1", and anything with "_domainkey" or "_dmarc" in the name. Why changing your website can break email explains each.
Set up the domain at the new DNS company first. Many will scan and import your existing records. Check the import line by line against your screenshot. Imports miss things.
Add anything missing by hand, and remove any default records the new company added that point to its own parking page, unless you want them.
Only then change the nameservers at your registrar, replacing the old names with the new ones exactly as given.
Wait. A nameserver change can take up to a day or two to be seen everywhere. During that time, some visitors are still asking the old company and some the new one, which is why both sets of records need to match. How long a domain change takes explains the wait.
Test email in both directions and the website on a phone with Wi-Fi off.
Keep the old DNS account open for a week before deleting anything there.

Signs you are editing in the wrong place

Owners lose whole afternoons to this. If any of these happen, the records you are editing are not the ones being used:

Your registrar shows a message like "DNS is managed elsewhere" or greys out the DNS section.
You change a record, wait several hours, and nothing changes anywhere.
Your registrar's DNS screen is empty, or shows only a parking record, while your website and email work fine.

Look up your nameservers again and log in to that company instead.

A quick decision guide

New website, same email: change records.
New email, same website: change records.
New provider insists on nameservers: change nameservers, after copying everything.
Old host or designer account closing: move the records somewhere you control, then change nameservers.
Not sure: change records. It is the smaller, more reversible step.

What to do this week

Look up your nameservers and write down which company they belong to.
Log in there and screenshot every record.
Decide, using the guide above, whether your next change is a record or the nameservers.
If it is the nameservers, set up the new DNS company and compare records before switching anything.

If the change you are planning is a new website, you can see your site rebuilt first and then make the one or two record edits it needs.