Hi there welcome, I am by far not the most knowledgeable, butI was a hard gainer also, here is a few tips, start montioring your caloric intake, and increase it by 200 calories a day, if you dont start gaining add another 200 calories, and you Will gain weight eventually when you find the right balance.
For supplements good old protein cannot be beat , some will disagree. Creatine is good, look around the board for the best creatine thread, some creatines have like No explode in them or something and increase your after workout pumps so it feels better after a workout, the feeling of accomplishment is higher so to speak. I would avoid steroids until you get your training and diet down pack, if you cant gain weight with food you wont gain anything worthwhile with roids. EAT TRAIN SLEEP. words to live by, once you start getting in the groove and putting on some pounds and have a good workout system then you can think about steroids, lets just say I did some M1t not to long ago and I severly regret it.many people will agree here if you cant gain without roids you wont with them.
Good luck and be determined. determination sets the bar, undetermined fail determined succeed and look great and feel great. feel free to ask anyquestions and stick around the board, most people are friendly and willing to help.