Hi,
Yes, you need to leave the values area empty in the filter. The filter will automatically use the values of the custom field in that case.
The values area in the filter is for when you have a text input field with numbers and you want to provide a range selector in the filter.
For example, if you have a text custom field with values from 0 to 100 entered in the products, you can enter there 20, 40, 60 and 80. Then, the filter will display the choices below 20, 20 to 40, 40 to 60, 60 to 80, above 80. But that only works with numbers, obviously.