if you want to put on muscle mass, weights is the obvious way.
You want to be doing heavy weights, 3 sets where you are fatiguing between 8 - 12 reps, and by fatiguing i actually mean you cannot physically do anymore, your muscles won't alow it. Leave about 30sec - 1min break between each set.
You should be on a high protein diet for this type of exersion, and i recommend that you cycle muscle groups you do, ie. don't do the same muscles 2 days in a row, you'll kill yourself.
MAKE SURE HAVE A WARM UP BEFOR HAND AND STRECH AFTERWARDS.
If you are working predominantly on your upper body, then a quick 5 min on the rower is a good warm up, trying to keep your speed above about 35, consistently over the 5 mins.
Your streches afterwards should not be rushed, personally, i really enjoy streaching, but I know that alot of people don't, but seriously, streaching is so so so important, i can't say it enough.
Drink lots of water afterwards, im talking more than 1.5 litres, and have a banana before you go to bed that night. This will help in the re-building (ie. growth) of the muscles.
Some supplements I recommend are weigh protean powder. Theoretically you should be having it instead of meals, but thats really only subtable if you work out like, 5 times a week or more. I find it good just to have before bed after you've had a work out. Drink too much without the apropriate amuont of exercise and you will get protean pimples on your arms, which scar.
Another one you can try is Creatin Monohydrate. Be careful with this, again, if you are not working out more than 5 times a week, you would only take it before a workout. I have a few friends who can't take it because their body seems to have a disagreement with it.
Basically, it gives your body more pc and so you can generally get in a couple more reps...its pretty cool, like, you dont really feel tired when you work out, but the down side is that you can quite easily strain/pull/tear a muscle withut realising it until later due to not really being able to feel the stress you put on it.
But all in all, my best advice to you is to o to a gym and see a trainer who works there, hey will tell you everything you need to know.