Explanation:
Go to HOME --> Azure Active Directory --> Devices --> Device settings.

Open Apple Safari and navigate to Azure Active Directory Device Registration service Over-the-Air Profile endpoint for iOS devices.
https://enterpriseregistration.windows.net/enrollmentserver/otaprofile/<yourdomainname>

Where <yourdomainname> is the domain name that you have configured with Azure Active Directory.

https://enterpriseregistration.windows.net/enrollmentserver/otaprofile/xavierdilipkumar.com

Open Apple Safari and navigate to the Device Registration Service (DRS) Over-the-Air Profile endpoint for iOS devices.
https://adf1s.contoso.com/enrollmentserver/otaprofile

1. Log on to the webpage by using a domain account credentials
2. You are prompted to install a profile. On the Install Profile screen, click Install.
3. When prompted to confirm installation of the profile, click Install Now.

4. If your device requires a PIN to unlock the device, you are prompted to enter your PIN.
5. The profile installation is finished when you see the Profile Installed screen. Click Done.
6. Return to Safari. A message informs you that you can close or leave Safari.

Goto HOME --> Azure Active Directory --> Devices --> All devices

Explanation:

By default, applications registered in an Azure AD tenant are available to all users of the tenant who authenticate successfully.

To restrict registered apps from users in Azure AD tenant:
Go to HOME --> Azure Active Directory --> Enterprise applications --> All applications --> <select app> --> Manage - Properties --> "User assignment required?" to Yes

Explanation:

Go to HOME --> Azure Active Directory --> Custom domain names --> Add custom domain --> Enter your custom domain name  --> Add domain

To use xavierdilipkumar.com with Azure AD, create a new TXT record with your domain name registrar using the info provided in the screen

Click Verify

Explanation:

Managed domain is the normal domain in Azure AD and can be deployed either through "Password Hash Sync" or "Pass Through Authentication" with Single Sign On.

Federated domain is used for Active Directory Federation Services (ADFS). The federation trust will make sure that the accounts in the on-premises Active Directory are trusted for use with the accounts in Azure AD with Single Sign On.

Deployed through WS-Fed and WS-Trust:
WS-Fed: This protocol is required to join a device to Azure AD.
WS-Trust: This protocol is required to sign in to an Azure AD joined device.