i'm six four. i used to be six four 155 (yeah scary i know). now i'm six four 195. Here's how I got to where I am:
Protein-rich foods. I find it to be much easier to add weight then take it off than to add muscle without adding any fat. Peanut butter, milk, tofu, etc--but most important is that you eat.
The absolute most important thing for you to do is to work out using free weights, and to do lifts that involve moving two joints at the same time. I bought weights and a bench; it's not that expensive and it's certainly worth it. Not only is it cheaper than a gym membership, if the weights are right there you'll be more motivated to lift 'em
as i did it, and again most of my basis is empirical evidence stated above, here are the important lifts:
for legs, i did squats (muy important), roman dead lifts, lunges, and calf raises. the same day i'd do abs--since i was interested in gaining weight, i did weighted situps (situps with a big frickin' plate on your chest).
for upper body i did dips, pullups, shoulder press, bench press, standing rows. Sometimes i'd add curls.
The key is to start slowly, to make sure you stick to your schedule, to write everything down, and only add 5% a workout. If you're lifting to failure your first workout you'll hurt yourself.
Also, change your routine every now and again.