ensure

I have a fast metabolism and I would LOVE to gain weight. I'm tired of looking in the mirror and hating what I see. I'm tired of people telling me I look unhealthy and like skin and bones. I want to try ensure. But someone told me that's for people who don't eat at all to gain weight or something. So would it be ok for me to continue to eat my three meals a day or whatever and drink ensure too? I want to gain about 20 pounds. Please help. Thank you in advance. 😊