Hi, Court!
I know it can be overwhelming in the beginning. The good news is that just a few changes can help give some results and set up healthy habits. Over time, you can keep tweaking.
For exercise, the most important thing is finding something you enjoy so that you'll keep up with it.
Walking is an excellent exercise for weight loss. That's because, unlike most exercise, studies show it doesn't trigger an increase in appetite. That makes it much easier to simultaneously cut down your calories. My brother lost over 100 pounds and his only cardio was walking. He was really committed to his walking though: walked at least an hour every single day. You may not want to do as much, and that's fine. But definitely give some walking a try! Starting out with 15 minutes on the treadmill at a 3-3.5 mph pace should be doable and enough to break a light sweat.
Down the road, I'd suggest adding in exercise that combines cardio with strength training. In my experience, that's the most effective way for dropping pounds. In the beginning though, it's really not necessary and probably would be unpleasant.
Idk how you currently are with water, but if that's not your main source of hydration, that's another valuable change to make early on. The general advice is to cut your weight in half (using pounds) and drink that in ounces. So a person who's 250 lbs, for example, would drink 125 ounces a day. If you drink your calories (soda, juice, etc), it's helpful to cut those out and replace with water and other 0 calorie drinks, like tea.
As far as how to eat...There are many possible ways of eating out there. I think it's important to first honestly track what you're eating for at least a few days so that you can get a sense of your current calories. The basic science is that it takes 3500 calories to lose 1 pound. You can accumulate those calories by saving them; that is, eating 3500 calories less than you normally would over the course of a week. Or, you could burn those calories by burning 3500 more calories than you normally would. That would be a ton of exercise though, and as I mentioned before, intense exercise can be counterproductive to weight loss b/c it triggers an increase in appetite. Another option, and I think what most people would agree is the healthiest, is to create that 3500 calories deficit through both eating less and moving more. A doable and sustainable system could be burning an extra 100 calories a day through walking (so 700/wk), and saving the other 2800 calories through eating less (so 400 fewer calories a day). If you track your food and find that you'd be ok with cutting down your current calories by more than 400 a day, then great - you'll lose at a quicker pace.
I generally think it's best to not drop too low though for a whole assortment of reasons.
It would be great if weight loss always went exactly according to that "3500 calories = 1 pound" formula, but unfortunately things like hormones, water weight, the body reacting to and resisting weight loss, etc can all make it a far from precise process. Overall though, barring health problems, it does work.
Good luck! Sorry if it was too numbers heavy or anything!