Congrats on wanting to change your fitness level. My suggestion is to try and incorporate a bit of walking into your everyday activities.
- If you drive to a shopping center/mall, park farther away from the door
- 'Pay' for each meal with a five minute walk beforehand, after the habit is established, increase to 10 minutes or longer
- If you work in a multistory building, walk up one flight of stairs everyday
- Sign up for walking tours, nature walks, orienteering competitions
- Go hiking. It's more interesting to go for a walk in the woods than the same boring walk around the neighborhood
- Listen to audiobooks while walking

The simplest and best diet recommendation I've ever gotten was by Michael Pollan:
"Eat food. Not too much. Mostly plants."
By "food" he means food with minimal processing. If it comes out of a package and has more than five ingredients on the label, then it probably should be avoided. Buy ingredients and cook your meals, and avoid packaged meals and snacks. Another food rule from Pollan is "don't eat any foods you see advertised on TV."

Get more active and eat healthier food, then start working on portion control. Gradually increase your exercises to include some strength training and more activities that burn calories.