The next thing you need to do is not panic. Exercise in moderation helps. You are physically out of condition so there's no way you're going to run a marathon or anything like that.
Start off with walking to the shops and back. It's harder than you think. Don't use a shopping trolly. Carry your bags. Don't get them delivered. By the time you get to the shops and back you'll feel knackered. Tough!
You can also have a look around the house you live in. Physical exercise is the second most important aspect to reducing weight and doing those neglected chores around the home are a good way to start.
Stairs are an ideal way to get fit. Use them. However use them for exercise. Stand at the foot of the stairs and place one foot on the next step then climb that step so both feet are on it. Now remove one foot from the step and step down again. Repeat again and again, this time a little quicker. If you climb the step 100 times a day in sessions of 50 and slowly increase, you will improve your cardio vascular activity. This means that your heart will pump blood and oxygen around your body a little quicker and help condition your body to accept mild exercise as a way of improving the overall tone of your physiology.
Don't go and do too much to start with. Work up to it. You'll find it's harder than you think. That's because your body is so out of condition and you need to pace yourself.