To create a new Azure AD Tenant that is isolated from the root tenant. We access our current Azure AD Tenant and then click on Create a Tenant.
Click to the next page.
Then, select the first option - Azure Active Directory.
NB: Azure Active Directory (B2C) depends on a scenario whereby you want to provide your Organization specific applications to clients but don't want them to have User accounts within your main Azure AD tenant.
Next, set a unique domain name for your new tenant.
After creating the new tenant, you will be able to switch to it.
You should also note that you do not need a new subscription to create or work with a New Azure AD tenant running on the Azure AD Free tier. For Azure AD P1 & P2 tiers, you definitely need a subscription to extend to those additional features that they provide.