As gt said, lift heavy-3-5 sets, 6-10 reps.
You can continue cardio but you need to get enough calories.
I trained for and completed a 100 miler on my handcycle while benching 315 lb at a bodyweight of 185. My weight remained stable throughout.
DO NOT fall prey to the lure of "miracle potion" supplements. The only thing they make bigger are the sellers' bank accounts.
You only need three supplements.
Protein, if you have trouble getting enough. A simple whey or whey/egg will do fine.
Multivitamin/mineral supplement-RDA doses are fine. Hypersupplementation is worthless.
Creatine-will not make you bigger on it;s own but does allow more work to be done.
"To give anything less than your best is to sacrifice the Gift."