Summary
You can use a Google Ads manager account to manage multiple Google Ads sub-accounts in one place.
You can't create campaigns or advertise products directly with a manager account, but you can use it to create campaigns on behalf of a sub-account that you manage.
Manual steps
- Sign in to the Google account you want to use as a manager account.
- Visit the manager account page, then click Create a manager account.
- Name your manager account. This is the name that your merchants see as their manager in the Access & Security tab of the Google Ads UI.
- Choose how to use the account. If you need to manage sub-accounts on behalf of other advertisers, choose "Manage other people's accounts".
- Select your country and time zone. - The time zone you select is used for reporting and billing, and you can't change it later. We recommend that you choose the time zone your business is based in. 
- Choose a permanent currency for your account billing. - We recommend that you choose the currency you use for business. Sub-accounts are billed in their own currencies. 
- Click SUBMIT. 
Automatic steps
Not available for this process.
You can't create manager accounts through the Google Ads API. You can use the API to create sub-accounts and link them to an existing manager account.