Perform the following steps:

1. Open the Nessus web client.
2. Log in to the Nessus client with the user that you created during installation.
3. Perform a simple network scan on the virtual machine and open the scan results:

4. Navigate to the export functionality and select the Nessus format to download the .nessus version of the report:

5. Navigate to the export functionality and select the Nessus format to download the HTML version of the report by selecting the required options:

6. Navigate to the export functionality and select the Nessus format to download the CSV version of the report:

7. Navigate to the export functionality and select the Nessus format to download the Nessus DB version of the report:

Enter a desired password and click on Export to download the Nessus DB file with the extension .db.