You do not create a standard object, since it already exists in your org. What you do is customize it. Here is how to extend a standard object such as Account or Contact in Object Manager using the Lightning Experience setup.
- Open Object Manager
From Setup, type Object Manager in the Quick Find box and select it. You will see every standard and custom object in the org. Click the standard object you want to customize, for example Account.
- Add a custom field
Select Fields and Relationships, then click New. Choose a data type, give the field a label, set the length or options, and save. The new field gets a __c API name even though it lives on a standard object.
- Adjust the page layout
Select Page Layouts, open the layout, and drag your new field onto the appropriate section. Set whether it is required or read-only on that layout, then save so users see the field where it makes sense.
- Add a validation rule
Select Validation Rules, click New, and write a formula that returns true when the data is invalid. Provide an error message and location. This enforces data quality on the standard object without any code.
Where you add custom fields, lookups, and master-detail relationships to the standard object.
Controls which fields and related lists appear, and their order, for users assigned to that layout.
Lets one standard object support multiple processes with different layouts and picklist values.
Set per profile or permission set to hide or expose individual fields independent of the layout.
- You cannot delete a standard object or change its API name, though you can relabel it in the UI.
- Some standard fields are required or read-only and cannot be removed from the object.
- Recreating a standard concept as a custom object breaks integrations that expect Account or Contact.
- Custom fields on standard objects still count toward the per-object custom field limit for your edition.