Practically these are the steps, as in the pictures attached:
1. Click on Sharing
2. Click on WebDAV tab
3. Click on Add WebDAV Share button
4. Write the share name; this will be part of the address. In the example below is MyShare.
5. Optionally write a coment.
6. Select the directory you want to share. In the example below is /mnt/SPACE/Ludo.
7. Click on OK button
8. Click on Services
9. Click on the wrench icon near WebDAV.
10. Select the protocol. In the example below is HTTP
11. Insert the port number for the service. In the example below is 3128. This will be part of the address.
12. Insert the password for the webdav user. It is needed for authentication later.
13. Click on OK button.
When you open in a browser
http://Freenas-IP:port/sharename you'll get similar to what you see in the last picture. In the example below the address is
http://10.1.150.210:3128/MyShare
Hope this is what you asked for.