Meta Business Manager is a tool that helps you organise and manage your business on Facebook. You can navigate to your Business Manager by signing in to your personal Facebook profile and going to business.facebook.com/settings/pages.
Some additional links that may be helpful:
How to set up a Facebook Business Manager: https://www.facebook.com/business/help/1710077379203657?id=180505742745347
How to add your local store's Facebook pages to your Business Manager: https://www.facebook.com/business/help/720478807965744?id=420299598837059
How to add Instagram accounts to your Business Manager: https://www.facebook.com/business/help/1125825714110549?id=420299598837059
How to add a team member to your Business Manager: https://www.facebook.com/business/help/2169003770027706?id=2190812977867143
How to add ad accounts to your Facebook Business Manager: https://www.facebook.com/business/help/910137316041095?id=420299598837059