Okay, here we go…
The whole “leg day,” “back day” is what we call the bro-split. For beginners, which is what you are, such a split is not advised. It’s too much isolation work. You should be focusing on full-body compound lifts. Compound movements include squats, deadlifts, overhead press, bench press, and bent-over barbell rows. If I were you, I’d look into StrongLifts 5×5 – it’s a fantastic program that is specifically designed for beginners to build strength quickly. You don’t need to spend any money, buy a book, etc. This has some information about it, but I have a pdf that I could send you somehow with everything you need to know. The best part of 5×5 is that it’s simple: it’s just the five moves I mentioned, three per day, three days per week. It’s a 12-week program, but you can do it until you stall out, at which time you can move into an intermediate program like Madcow or Wendler’s 5/3/1, which includes accessory lifts outside of the main compound lifts. Some isolation work here is perfectly fine, but compound lifts are paramount, always.
Stay away from weight machines! At least in the beginning. No leg extensions/curls/presses, no lat pull-down machine, no pec fly machine, no crunch machine, no curl machine, etc. Your body, a barbell, and weight plates are all you need. Of course, you’ll need the bench and rack to do bench presses and rack for squats, but you get my point. Cardio and/or yoga can be performed on non-lifting days if you wish.
Weight loss happens in the kitchen. The reason you gained the weight back when you started your job isn’t because you aren’t working out. It’s because your body is naturally burning less calories because you’re sitting on your tush all day. So, your new number of calories burned daily (TDEE) is less than the number of calories you’re consuming. Know this: lifting is not for calorie burn. Cardio burns more calories than lifting, but lifting is what makes your body look good (the “definition” you’re talking about, and avoiding the “skinny fat” look). Lifting will help you lose weight, but don’t expect a huge calorie burn out of it. Furthermore, you need to be eating a sufficient number of calories. If you happen to be one of those people that refuses to count calories, that’s your choice, but you’re asking for trouble. If you’re not logging your food, you have absolutely no idea how much you’re eating. Eat too little and your lifts will suffer. Eat too much and you’ll keep gaining weight. It’s just math. There are plenty of sites/apps that allow you to easily log your intake. You can use Scooby’s TDEE calculator to determine the number of calories you should be eating to achieve your goal. I’d also invest in a food scale, because measuring cups are very inaccurate for solids.
Please for the love of all that is holy don’t fall into any of these traps: low-carb diets, intermittent fasting (or any fasting), juicing, cleanses/detoxes, all-cardio workouts, low-fat diets. It’s all bullshit. All of it. It’s calories in vs. calories out. Carbs are not bad, they’re necessary. Fat is not bad, as it’s also necessary. A balanced diet is what you need – don’t cut anything out. Food is fuel, and your body needs it. Fuel your body properly and it will thank you. You do not need to eat vegetarian/vegan, “organic,” gluten-free, dairy-free, etc. You don’t need to eat “clean” (whatever that means). Look up IIFYM (if it fits your macros) and, if it seems interesting to you, I’ll explain it further. Protein is extremely important. The calculator I link will give you an estimated number of grams of protein to eat daily, but .75–1g per lb of body weight is pretty standard.
I’m going to be late for work if I keep typing, but here is my blog if you’re interested. There’s only two posts, but go down to the first one and read it, especially my tips at the end. I’m going to come back once I get to the office because I wanted to comment on another jelly’s response.