When you add a lookup field in an object to another object, the lookup object will become the parent object, this is applied for both Standard and Custom objects.
In this example: I have a custom object called Region with a lookup field to Account.
And if we go to the Account page layout, we can add Region as a related list.
How to change the "Regions" label to something else? Let's say it should be called "Supported Regions".
Let's go back to the Regions object, open that field and change the "Related List Label"
Refresh the account page and now should show "Supported Region"
Bonus requirement: the New button should not be in the related list.
- Go to Account page layout
- Click Related Lists on the left panel, scroll down to the related list object
- Click properties icon, click Buttons, then untick New checkbox