How do I start running when I am completely out of shape?

Start with walk-run intervals rather than trying to run continuously. Go out for 20-30 minutes and alternate between 1-2 minutes of slow jogging and 2-3 minutes of walking. The jogging pace should be slow enough that you can hold a conversation. Do this 3 times per week, giving yourself rest days in between. Each week, gradually increase the running intervals and shorten the walking breaks. Most beginners can work up to running continuously for 30 minutes within 6-8 weeks using this approach. The biggest mistake people make is going too fast too soon, which leads to burnout or injury. Slow down more than you think you need to, and consistency matters far more than intensity at the start.