Running is not just physical endurance, but includes building up and increasing flexibility of the muscles, proper form, timing, and developing mental endurance.
What you may need to do is start from the bottom and build yourself up. Build up leg, calves, and feet/ankle strength. Expand into your back and sides because when running your body will also move slightly.
When you start building yourself up, running is probably the last thing to come.
1) just start walking on the treadmill. Comfortable pace. See how long you can go. 5 minutes? 10? Try turning the walk to a brisk walk like you're trying to not look like you're in a hurry, but you want to get somewhere faster.
If you're early on and barely even breaking a sweat then you can likely move to the next level.
2) Jog. Just jog. If you compare walking to jogging your knees go higher.
That should be enough over time to get some basic conditioning into you for running. There are exercises to compliment the build up, including and not limited to: jumping jacks, squats, and heel raises. Squats and heel raises you can hold on to a railing or chair to reduce the weight. Eventually you can move to do them without assistance.
When running you need to control your timing (aka pace). Don't worry about going 12km/hr. Cars burn more fuel the faster you try to go, the same with your body. Everything is a slow build up to increasing your speed, but to do that you need to start slow.
