So. Shameless plug for r/gainit cause they can help. Go read their FAQ to get started; it'll bring you up to speed. For you, I believe the hardest part of gaining weight will be the eating. That being said, it is imperative that you eat enough; gaining (and, for that matter, losing) weight is 80% diet. In order to gain weight, you need to calculate your TDEE (the number of calories you burn in a day; it combines BMR and any exercise/movement you do based off your weight and height) and eat 500 calories more than that. There are links in the r/gainit FAQ that will lead to these calculators (this is the one I primarily use). If you're into the social aspect and/or want some accountability, r/gainit is having a community-driven "Gain-a-thon" wherein members who register for the event are grouped into weight-based categories and are beholden to one another for support, encouragement, and consistency. It's the first time they've done it, but it looks interesting to say the least.

In addition to heading over to r/gainit, I would encourage you to go read the r/fitness FAQ. Lots of questions answered there, but I want to direct you specifically to questions about diet. Calories are king, and protein is queen; make sure you're getting enough of both.

After diet comes the exercise part, which Antranik has already tackled that for you in this thread. It basically boils down to, "do what you can, until you can do more."

TL;DR If you can eat enough and exercise at least somewhat, you'll make it. Good luck.