Eat a lot to gain mass

Starting to learn something new at the age of more than twenty can sometimes be confusing. I am twenty six years old now and I begin to visit the gym regularly. Maybe I am not the best material for an athlete - I have never had actually anything to do with sport in any meaning. I have spent most of my life in front of my notebook screen earning money and playing stupid computer games. Now when the opportunity to get some activity has appeared, the advices I got seem totally different than the priorities I have always imagined. I have never thought that I will have to eat a lot to gain mass. They told me that I needed to gain mass to train in the gym, otherwise there will never be any results. You know what I mean? I don"t know what to think about it - what do they mean gain mass? What do they mean eat a lot? Have you ever heard of a kind of sport that is about eating? Maybe it is sumo, what if they want to make a sumo fighter out of me? Oh I need to think it all over a couple of times to make the right decision. What sense is there in doing something I don"t even believe in? on the other hand I also think about a situation in which it turns out that my advisors were right and I will look like a model after following their remarks. In fact I will never know without trying. Maybe I should give it a small chance?