How to get fat? i'm a thin man. i'm 165centimeters, but only 46kilograms.

Diet and muscle mass: To gain weight you have to consume more calories than you are burning. Do this in a healthy way though. Don't choose junk or fast food. Keep a well balanced diet and make sure you are getting all the nutrients you need. Don't cut out exercise as it is very good for you. Weight lifting and other muscle building exercises can help you increase your body mass.

See PCP: See pcp to rule out any medical problems that might keep you thin (ex celiac disease, over active thyroid) and if no medical problem is found see a dietician who can review your diet and help u set up a healthy meal plan that would result in weight gain.