Carry out the following steps to set a default name when creating an opportunity using a field update workflow rule:

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

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

3. Navigate to the workflow rules customization setup page as follows:
   Process Automation | Workflow Rules.
4. Click on Continue (if shown).

5. The Continue button is found on the Understanding Workflow page (if this appears), as shown in the following screenshot:

We will be presented with the Step 1: Select object page.

6. Select Opportunity and click Next, as shown in the following screenshot:

We will be presented with the Step 2: Configure Workflow Rule page.

7. Enter Set Opportunity Name in the Rule Name field.
8. Optionally, enter a description in the Description field.
9. Select the created, and every time it's edited option from the Evaluation Criteria options list.
10. In the Rule Criteria section, set the Run this rule if the following option to formula evaluates to true.
11. Enter the following formula in the formula editor:

NOT( CONTAINS( Name, Account.Name ) )

12. Click on Save & Next, as shown in the following screenshot:

We will be presented with the Step 3: Specify Workflow Actions page.

13. In the Immediate Workflow Actions section, set the Add Workflow Action option to New Field Update, as shown in the following screenshot:

We will be presented with the New Field Update page.

14. Enter Opp Name Update in the Name field.
15. Accept the default value in the Unique Name field, which is automatically set as Opp_Name_Update.
16. Optionally, enter a description in the Description field.
17. Set the Field to Update to Opportunity Name.

We will be presented with the Specify New Field Value section.

18. Select the Use a formula to set the new value option.
19. In the formula editor box, paste or enter the following formula:

Account.Name & " " & Name

20. Click on Save, as shown in the following screenshot:

We will be presented with the Step 3: Specify Workflow Actions page.

21. Click on Done, as shown in the following screenshot:

We will be redirected to the new Workflow Rule where we can activate the rule.

22. Finally, click on Activate, as shown in the following screenshot:

If there is no default workflow user currently set, a user will need to be chosen and you will be alerted with a warning message, as shown in the following screenshot:

23. Click on OK.

If there is no default workflow user currently set we will be re-directed to the Process Automation Settings page where we can set the Default Workflow User, as shown in the following screenshot:

24. Set the Default Workflow User.
25. Click on Save.
26. We are finally re-directed to the Workflow Rule Detail page with the Active checkbox set, as shown in the following screenshot: