I'm what's technically known as a geezer which means my exercise opportunities are restricted. Three years ago I needed to lose weight and dropped 50 lbs / 23 kg in six months.
I started eating smaller portions, stopped snacking, and switched to healthier foods. And I WALKED.
I started off doing 4 km / 2.5 miles every day and built that up fairly quickly to a minimum 6 km a day.
That's all you need to do. The amount of time you spend will depend on how quickly you walk.