Add detailed explanation of zone apex and reorder concepts

Author: RebeccaTamachiro

src/content/docs/dns/concepts.mdx

@@ -9,6 +9,8 @@ head:
 
 ---
 
+import { Details, Example, GlossaryTooltip } from "~/components";
+
 This page defines and articulates key concepts that are relevant to the Cloudflare DNS service and are used in this documentation. For more concepts and broader descriptions, refer to the [Cloudflare Learning Center](https://www.cloudflare.com/learning/dns/what-is-dns/).
 
 ## Domain
@@ -39,12 +41,18 @@ This is important because the performance of such authoritative DNS services det
 
 It is also possible that one same company will use more than one DNS provider. Usually, this relates to making a domain more resilient - if one provider faces an outage, the nameservers operated by the other DNS provider will most likely still be available.
 
-In this context, you can have a primary DNS setup, when you use Cloudflare to manage your DNS records, or a [secondary DNS setup](/dns/zone-setups/zone-transfers/cloudflare-as-secondary/), when your DNS records are managed on a different provider and Cloudflare simply receives zone transfers containing your DNS records.
+In this context, you can have a primary DNS setup, when you use Cloudflare to manage your [DNS records](#dns-records), or a [secondary DNS setup](/dns/zone-setups/zone-transfers/cloudflare-as-secondary/), when your DNS records are managed on a different provider and Cloudflare simply receives zone transfers containing your DNS records.
 
 When you have a primary DNS setup, you can either use only Cloudflare (also known as [Full setup](/dns/zone-setups/full-setup/)), or you can use Cloudflare and another provider, where the other provider is the one to receive [outgoing zone transfers](/dns/zone-setups/zone-transfers/cloudflare-as-primary/) from Cloudflare.
 
 Finally, as Cloudflare also works as a [reverse proxy](/fundamentals/concepts/how-cloudflare-works/#how-cloudflare-works-as-a-reverse-proxy), [partial (CNAME) setups](/dns/zone-setups/partial-setup/) can be used when you do not want Cloudflare to be [authoritative](#authoritative-dns) for your domain but you still want to proxy individual subdomains through Cloudflare.
 
+## DNS records
+
+DNS records are instructions that live in the authoritative DNS servers and provide information about a [zone](#zone). This includes what IP address is associated with a particular domain, but can also cover many other use cases, such as directing emails to a mail server or validating ownership of a domain.
+
+For more details about using DNS records within Cloudflare, refer to [Manage DNS records](/dns/manage-dns-records/how-to/create-dns-records/) and [DNS record types](/dns/manage-dns-records/reference/dns-record-types/).
+
 ## Zone
 
 DNS zone is an administrative concept used for delegating control over a given domain and its subdomains. Read more in the ["What is a DNS zone?" Learning Center article](https://www.cloudflare.com/learning/dns/glossary/dns-zone/).
@@ -53,11 +61,69 @@ For the purpose of this documentation, keep in mind that each domain added to a
 
 Also, different Cloudflare products and features are configurable at the zone level. Refer to [Fundamentals](/fundamentals/setup/manage-domains/connect-your-domain/#domain-configurations) for details.
 
-## DNS records
+### Zone apex
 
-DNS records are instructions that live in the authoritative DNS servers and provide information about a zone. This includes what IP address is associated with a particular domain, but can also cover many other use cases, such as directing emails to a mail server or validating ownership of a domain.
+Zone apex refers to the domain or subdomain on which the control of DNS records starts.
 
-For more details about using DNS records within Cloudflare, refer to [Manage DNS records](/dns/manage-dns-records/how-to/create-dns-records/) and [DNS record types](/dns/manage-dns-records/reference/dns-record-types/).
+<Details header="Example 1">
+<Example>
+DNS management for **example.com**:
+
+| Type | Name    | Content      | Proxy status | TTL    |
+| ---- | ------- | ------------ | ------------ | ------ |
+| A    | `blog`  | `192.0.2.1`  | Proxied      | Auto   |
+
+Zone apex: `example.com`
+
+Full record name: `blog.example.com`
+
+</Example>
+</ Details>
+
+<Details header="Example 2">
+<Example>
+DNS management for **sub.example.com**:
+
+| Type | Name    | Content      | Proxy status | TTL    |
+| ---- | ------- | ------------ | ------------ | ------ |
+| A    | `blog`  | `192.0.2.1`  | Proxied      | Auto   |
+
+Zone apex: `sub.example.com`
+
+Full record name: `blog.sub.example.com`
+
+</Example>
+</ Details>
+
+Usually, the zone apex coincides with the <GlossaryTooltip term="apex domain">apex domain</GlossaryTooltip>, as shown in Example 1. Example 2 refers to [subdomain delegation](/dns/zone-setups/subdomain-setup/), which is only available to Enterprise plans.
+
+To create a DNS record at the zone apex, use `@` for the record **Name**. For details, refer to [How to](/dns/manage-dns-records/how-to/create-zone-apex/).
+
+<Details header="Record at the zone apex">
+<Example>
+DNS management for **example.com**:
+
+| Type | Name    | Content      | Proxy status | TTL    |
+| ---- | ------- | ------------ | ------------ | ------ |
+| A    | `@`  | `192.0.2.1`  | Proxied      | Auto   |
+
+Zone apex: `example.com`
+
+Full record name: `example.com`
+</Example>
+
+<Example>
+DNS management for **sub.example.com**:
+
+| Type | Name    | Content      | Proxy status | TTL    |
+| ---- | ------- | ------------ | ------------ | ------ |
+| A    | `@`  | `192.0.2.1`  | Proxied      | Auto   |
+
+Zone apex: `sub.example.com`
+
+Full record name: `sub.example.com`
+</Example>
+</Details>
 
 ## DNSSEC