Carry out the following steps to create a custom Credit Score field on the Account object:

1. Click on the Setup gear icon in the top right-hand of the main Home page, as shown in the following screenshot:

2. Click the Setup option, as shown in the following screenshot:

3. Navigate to the Account customization setup page, by clicking the following: Objects and Fields | Object Manager | Account | Fields and Relationships.

Locate the Fields & Relationships section on the right of the page.

4. Click New.

We will be presented with the Step 1. Choose the field type page.

5. Choose Number from the Data Type options.
6. Click Next.

We will be presented with the Step 2. Enter the details page.

7. Enter Credit Score in the Field Label.
8. Enter 3 in the Length field.

Accept the default option of 0 in the Decimal Places field, as shown in the following screenshot:

9. Optionally, enter a value in the Description field.
10. Optionally, enter a value in the Help Text field.
11. Click Next.

We will be presented with the Step 3. Establish field-level security page.

12. Select the profiles to which you want to grant edit access to this field via the field-level security. The field will be hidden from all profiles if you do not add it to the field-level security.
13. Click Next.

We will be presented with the Step 4. Add to page layouts page.

14. Select the page layouts that should include this field. The field will be added as the last field in the first two-column section of these page layouts. The field will not appear on any pages if you do not select a layout.
15. Finally, click Save.