You don't, that's not how they work. Symptoms and Alert Definitions are universal objects but Alerts can be controlled via policy to apply to as many or as few objects as you wish.
I agree with Chip here, that is how the product is designed however you could do the following:
(I have not tried this but it might be possible)
Create a symptom definition as needed such as (VM has CPU > 95%) and create another one for (VM has name x) or (VM is in folder y)
In your alert definition, put in both definitions with the AND rule.
If you are simply looking to create an alert notification, then create a new one and select both the object and alert definition filters.
Hope this helps.