Hello pookiefeb,
You can achieve this by using the Tag feature . This will help you to label or categorized the records. Tags are more powerful than a traditional category dropdown field because you can assign multiple tags to the same record.
You can also achieve this by adding a dropdown field to the screen. In the dropdown field you can add the list of the product or services, so when you go to New lead screen, you can select the product/service from the dropdown menu.
Hope this helps!
-Inder