Is Meditation And Concentration Mutually Exclusive?

I'm relatively new to mindfulness meditation and I've been having trouble focusing / concentrating during my sessions. Even thought my meditation sessions are around 10 - 20 minutes, I feel like my mind is just wandering. I've tried to really focus on my breathing but after a while I notice myself thinking about something else. I've read this article: How A Few Simple Things Helped Me Meditate Without Losing Concentration and it has helped me a bit. But I'm reading around other websites and people are saying that meditation is the opposite of concentration and if you're concentrating then you're not meditating. That meditation is expanding the mind while concentration is narrowing it and that the two are mutually exclusive. I feel lost on what I should be practicing.