Facebook Business Manager app - Business Manager is a product from Facebook that is intended to make it easier for business people to manage their fanpage accounts and advertisements.
It should be noted that Business Manager and Ad Account are the same. Ad accounts, Facebook Pages, and other apps are part of your Business Manager.
Here is a way how to get Facebook Business Manager app
First Visit the following link https://business.facebook.com/
Then a page like the image below will appear and click the CREATE ACCOUNT button to get started
Next will appear a page to create a business account like this. Complete your Business Name, Your Business Email Address, then click the Next button.
Next, your Business Information Details page will appear. Then add detailed information such as Country, Address, City, Province, Postal Code, Web Address, and also the purpose of Using Business Manager. Make sure you fill in correctly, if you have clicked the Submit button.
Next confirm your email. Please login to the email you just registered for Business Manager.
You will receive an email like this, please click the Confirm Now button
Then your Business Manager account has been created successfully.
When Business Manager is created, you can add Admin as an account, and can also manage facebook ad settings.