

Hey everyone! I am M22, and I have a pretty average or at least a skinny build. I wanted to work out and not only have a muscular build but, more importantly, be stronger and have more endurance. Although I want to get started, I'm unsure where to begin with exercise, as I am very new to it.
I wake up in the morning around 7 AM and sleep at 11 PM. I eat PB&Js, ham and cheese sandwiches, Kraft Mac n cheese, spaghetti, fruits, candy (sometimes), and fast food that (almost once a week).
I also drink soda, milk, water, and sometimes green herb tea.
I walk almost every day or at least 2-3 days a week.
One arm cannot do repetition (doctor's orders), nor is it as strong as my arm (the one I used to take the pictures).
What changes or things can I start to make improvements in?