Hi mate,
Exactly what Cate has already said. Eat lean healthy foods and remove most if not all added sugar (feel free to do this slowly as sugar is after all addictive and you will have cravings/withdrawals if you go cold turkey).
Walking is a great way to start exercising. I used to be very very fit; quite “buff” actually and to quote the simpsons “before the weight of the world crushed my spirit.” And I only ever had a bike and an old school chest expander spring dooflacky I borrowed from my father. Much later on I bought a 25kg dumbbell set and joined a gym but mostly i would walk and jog for my exercise.
Remember eating well, drinking HEAPS of water and exercises that are as close as possible to natural body movements are the best way to get your general fitness up. Lots of stretching, planks, lunges and squats are great for abdominal muscles, legs and glutes but Body fat cannot be targeted despite there being so many products that claim they can reduce your belly fat, butt, thighs etc. it’s all marketing mumbo jumbo.