I've been going to the gym 4 days a week (often just 2, but ideally 4). 2 upper body days, 2 lower body days.
For me, going to the gym means that I'm much more likely to do a full workout than if I stayed home. It's also easier to properly target all of the important muscle groups. Machines are a good place to start. Use lower weight than you think, and really focus on feeling the muscle and doing slow, controlled motions.
I just do protein shakes, which is maybe not enough. I definitely don't get enough calories, as I live alone and have a very hard time preparing food and eating a proper amount. Calorie surplus is important for building muscle. I've made very little progress because I keep losing any weight that I gain :(
I love typing 'yay kitty' on a new install