Hi Apricotton,
It sounds like you’re looking to get started.
You say that you’re very unfit, so the idea would be to start off gently, make it enjoyable and form a habit.
A good focus would be to work on two things: cardiorespiratory fitness and strength.
Cardio
The aim when getting started is to work in the following order: frequency, then duration and then intensity.
I’d stick to your walks, but aim to walk faster and up until a speed where you feel you’re working harder than a normal walk, but can still speak in full sentences. This should feel comfortable, even enjoyable. Try to increase how often you’re doing this and build up daily, even if it’s only 10 minutes. Over the weeks try to accumulate more time doing these walks than you did the week before.
This will build your aerobic base and increase something called your ventilatory threshold (the point you can no longer speak in full sentences). It means you’ll be able to do more for longer week by week, but it will be comfortable and enjoyable. It will also improve your ability to use fat for fuel.
Once frequency and duration are sorted you can then increase the intensity slowly by:
Incorporating hills walks or hikes
Add a weighted backpack
Try walk/jog (30s walk/30s jog)
Strength
Start very simply. Here’s some ideas from Rangan Chatterjee on a 5 minute kitchen workout.
Once you feel a bit more comfortable, you could buy a few things to add a bit more of a challenge: dumbbells, kettlebells etc Or, join gym and get a few PT hours to give you some guided sessions and a plan.