To get started, focus on implementing a few basic sound training and diet characteristics. Then with time you can explore and experiment with various additional ideas and approaches to tailor and refine your training and diet to your own body and goals.
In the gym, your first priority should be a focus on (re)learning the basic free weight movements: Deadlifts, Squats, Bench Presses, Overhead Presses, Chinups, Underhand Grip Rows and Standing Calf Raises. A variation of these should always be your staple movements. The neural grooves necessary for good form to become second nature are best trained with higher reps, like in the 12-20 rep range. Learning how to use your inner abdominals properly should be a priority as it can play a significant role in minimizing the chance of back pain or injury issues as well as being a limiting factor in your strength potential on the big lifts. You should also work some focused external rotation training in at least every couple of workouts as the rotator cuff of the shoulder is highly prone to injury.
To get started on the diet front, you want to focus on cutting out partially hydrogenated fats and refined sugars while being sure to get adequate daily fiber and at least 1 gram of protein per pound of lean bodyweight (bodyweight minus your bodyfat) a day spread out over at least 5-7 meals.
On the supplement front, the only supplements you'll really need starting out are multivitamins and Omega 3 oil for the essential fats.