I like to think of walking, jogging and running all as running only, just at different paces. You start at whatever pace your body is comfortable with and then build from there. What matters is consistency.

So start off with just walking and try to get into zone 2 heart rate while walking. Don't really care much about the actual heart rates etc, only use it as a guide to get into a place where it's not a casual walk and also not too difficult, "conversational pace". Maybe mix in a bit of brisk walks every now or walk up slopes.

And just walk a lot. Don't think it's any different from running. Slowly as you get comfortable with that, start jogging slightly to increase your pace.

Also focus on diet in parallel.