A focus group is good for evaluating a section of the overall product or service. Creating a focus group can take a number of different approaches, whether it is having a small group of users discuss what you want feedback on or whether you combine the focus group with a survey and allow multiple users to come through a set space in a span of time to give feedback.

 

More resources:

https://www.usability.gov/how-to-and-tools/methods/focus-groups.html

https://www.nngroup.com/articles/focus-groups/