Consistency is key. Start with basic, good nutrition and plenty of sleep. I would start with weight lifting, specifically Gym Styles.
If you want to get into serious shape, you have to start thinking about lifting heavier. Cardio is awesome for the heart and it has a myriad of good effects, but to change your body you need to lift and get out of your comfort zone.
Take stock of what you have. At the minimum you should have a barbell, the Troy Lite system is good to start with as it comes with 40 pounds, I'd try for sixty pounds though.
You need dumbells, 3,5,8,10,12,15,20 which will be great to start with.
Search for 25's and 30's when you are making great progress on Craigslist. Also think about getting Pace Weights, that are in increments of 1.5 pounds.
Get a real bench, not a step. Something that will feel comfortable against your back and is not too high so you can place the dumbells down on each side. I would also have a high step with at least 4 risers.
Think about your workout area and dedicate it to being a workout area so its not a major chore each time. This may be difficult, I totally understand this.
Honestly, the best program to me is STS for getting yourself into a different arena. Its an investment, and if I couldn't have that, I would go for Gym Styles.
You cannot underestimate what good sleep will do for you. Get enough protein, good grass fed whey protein, grass fed beef, salmon, greek yogurt, etc., Take your weight and multply that by .50 for a minimum and .70 for maximum amount of grams to take in per day.
Your intake of food will be critical and cannot be something you just do for a time being. Change it forever... Learn that food is for sustenance and not entertainment. Save that for Friday and Saturday nights if you need it, but still keep it in bounds.
I would have a good scale that is dependable and weigh yourself same time several times a week. You'll see yourself gain a pound after a hard lifting session which is good because your muscle have now swelled with water and are in repair/building phase.
Remember to switch things up, which is why I like Slow and Heavy and full body workouts like Muscle Max, Muscle Endurance, Power Hour. I love 4DS the premix that is full upper/lower body, its a killer workout.
You need cardio. The key is to find something you are passionate about and stick with it, but not all cardio is the same. Slow and steady is necessary, but HIIT is also necessary, to the point where you can't breath, that will force your body to adapt.
Write it down, start with your current weight and maybe a picture and definitely measurements and then stick with it. Your changes will be be evident.
Good luck, I can't stress again how much food, sleep and lifting heavy will change your body.
