We get this question a lot and there are so many ways to describe this and in different situations.
Understand that the resistance is not all arms! It also has to do with the connection between your arms and body, as well as your presence.
It may be confusing because sometimes we are told that we have to stay relaxed, but give resistance at the same time. You have to come up with a happy medium!
The best thing to do is become aware of what your body is doing/feeling and do a check-in to see if any parts are overly tense. Also, practice giving resistance and releasing it.
This is because we are not in a 100% constant state of resistance when we dance. We have to understand where, when, and how to use it!
Hopefully this video will help you!