Custom fields are created in Object Manager, one object at a time. The flow is the same for almost every type: pick the data type, name the field, then set visibility and which layouts show it. Here is the standard path in Lightning Experience.
- Open the object in Object Manager
From Setup, go to Object Manager and click the object you want, for example Account. In the left sidebar, click Fields and Relationships, then click New.
- Choose the data type
Select the field type that matches the data, such as Text, Number, Picklist, or Lookup Relationship. The type is hard to change later, so confirm it fits how the field will be queried and displayed.
- Enter the details
Provide a field label, which auto-populates the API name. Set length or precision, default value, help text, and flags such as Required, Unique, or External ID where they apply.
- Set field-level security
Choose which permission sets or profiles can see and edit the field. Tighten this now rather than accepting the default, especially for sensitive data.
- Add to page layouts and save
Select the page layouts that should display the field, then click Save. The field is live immediately and available in reports, SOQL, and the API.
The field type, such as Text or Picklist. It governs accepted values and behavior and is set before anything else.
The human-readable name shown on layouts and reports. Salesforce derives the API name from it on first save.
The permanent identifier used in code and integrations, auto-suffixed with __c for custom fields.
- The API name is permanent once saved. Relabeling is free, but the underlying API name never changes, so name it carefully the first time.
- A field hidden by Field-Level Security will not appear even if it sits on the page layout. Check FLS before assuming a layout issue.
- Changing a field's data type after it holds data can truncate or lose values. Review the conversion considerations before converting a populated field.
- Roll-Up Summary fields need a master-detail relationship. You cannot roll up across a plain lookup.