I'm 18 and I weight about 118 and I really want to gain weight a healthy one and today my brother got me mass-tech is there anything I should worry about?

Yes. Worry about anything that's not "food from the farm". Normal healthy people gain weight just fine, eating healthy foods that are not overly processed. Supplements are not needed. One's regular doctor can check to see if there is a hormonal problem or other condition, if a person is very underweight. (everyone should have a regular doctor to do check-ups and answer questions.).