HOW TO GAIN WEIGHT. Reply me in detail.

IAM 23 YEARS OLD MY HEIGHT IS 165 CM MY CURRENT WEIGHT IS 45 I HAVE A VERY LEAN BODY ..IAM TRYING TO PUT ON MY WEIGHT BT MY WEIGHT IS NOT INCREASING IAM A NON VEGETARIAN .. I USE TO HAVE TWO EGGS DAILY ONE GLASS OF MILK WITH B PROTEIN POWDER N USE TO HAVE GREEN BANANA DAILY N OTHER FRUITS LIKE APPLE MANGO OTHER THAN THIS DAILY BREAKFAST CHAPATI N SABJI AND NOON BROWN RICE NIGHT ALSO , AND EVE SOME SNACKS BT STILL M NOT ABLE TO PUT ON MY WEIGHT .. PLEASE SUGGEST ME TO PUT ON WEIGHT MY HANDS LEGS THIGHS ARE VERY THIN N EVEN PLEASE CLEAR ME THIS AFTER HAVING THESE FOOD Y THERE IS NO DIFFERENCE IN BODY ... PLEASE SUGGEST ME A DIET AND LET ME KNW IS IT GOOD TO GO GYM FOR THIN BODIES TO PUT ON WEIGHT QUICKLY .PPLEASE REPLY ME IN DETAIL.