I think Cicero's advice is a little specific and involved at this stage of your journey.
I'd recommend starting with walking more. Chose to walk every time that you have a choice between a 20-30 min walk or a 5 min drive. Try to walk for 20 minutes before or after dinner.
As for food (which is the most important part) I always recommend starting with the following 3 tips.
1. Stop drinking your calories. At all. Milk in your tea or coffee is it. No soda, no milkshakes, no juices. You can have up to 2 cans of zero sugar soda per day(to start). The rest of it should be water, sparkling water, tea, coffee, and no added sugar cordials. No energy drinks, sugar or no.
2. Think about what you're eating before you eat it. Writing a food diary at dinner time is very helpful here, but if you can't do that, just think about what you ate. Did it bring you shame or guilt? Did it seem excessive? Consider that a normal person eats 200-2500 calories per day, where do you think your day was at in terms of calories? Thinking about food is way underrated and leads to long term changes.
3. Don't eat after dinner. Nothing. Nada. No snacks, no fruit, no non water drinks.
Do these 3 really simple things for a month, plus the walking. None of these steps involve any kind of real sacrifice, but combined they're worth noticeable weight. If you can't do these things, making proper lifestyle changes later on will be hard. Once you've done all this for a month or so, I'd recommend counting your calories on an app, for just 1 week. It's a bitch, but do it. It'll give you a great idea of where you're at at that time. From there, reduce your portion sizes, limit snacks, limit eating out to twice a week ect ect. And then go to the gym, whish is a whole new kettle of fish.
A couple things to be wary off.
Don't start running or jogging. You're 22st, you'll injure yourself, or at best, be in pain and uncomfortable as fuck. Rowing or stairmaster for you my friend.
Lifting weight is an excellent idea long term, but i'd first focus your energy on losing weight. Working out is actually outrageously inefficient at burning calories compared to cardio. Once you're hitting the gym 3 times a week for cardio, you've lost some good weight and are eating healthier, THEN I'd recommend starting to hit the weights.