You say you want to gain as much muscle mass as possible. First you got to get your diet in order. Use the sticky "Clean bulking diet" in the Diet forum. To gain, you have to eat often... And when I say often, I mean really often!!! Every 2 hours you should think about eating and start to prepare something to eat... You must never be hungry... NEVER! You got to get in your mind that not eating for 4 hours straight is the worst thing that could happen in your life... Don't forget to eat as soon as you wake up. At that point, your body has been out of food for 8 hours, which is not good to gain mass.
Next, if you want to gain muscle mass, you gotta incorporate the three basic mass gaining exercises in your workouts:
- Bench press (On pec day)
- Deadlift (On back day)
- Squat (On leg day)
Those are the most important exercises to gain mass... Squat is the best one. Make sure you are taught how to do these properly... Especially the last two ones as they use the lower back which is at risk of injury without proper form.
Forget about the machines, and the fancy work... If you want to get big, you gotta use the freeweights. Dumbells, barbells and plates. These will develop your supporting muscles.
Last thing: SLEEP!!! At least 8 hours a night. Really important for recovery.
Hope you'll be doing good and welcome to the forums! Enjoy your stay