When setting up ERPNext for the first time, you’ll be prompted to create a new Company.
This will be company ABC. On setup, you’ll see the tax templates, ledgers, warehouses, etc created for this company.
Once this is done, go to the Company master and select an option that says Is Group. This will allow you to create new subsidiaries under ABC.
Next, create a new company from the company list. Here you’ll get an option of Parent Company. Select ABC here. This is how you’ll setup ABC Mumbai, Madurai and Bangalore.
Each company will have its ledgers, warehousing, etc maintained separately and you can view their finances individually as well. Based on this, you can assign permissions so that employees can view only their company data.