A "minor" is like a "major" in college, but it takes fewer classes to complete. It usually requires that you take about 5-6 classes in one subject.
You can use the words "major in" and "minor in" as verbs:
I majored in Art History.
I considered minoring in French, but I would have had to stay an extra semester to finish it up.
Because a college minor is not as important as a major, it's not as common to say that you "are" a (something) minor or that your minor "is" something. People usually use the verb form instead.