Especially beginners have to train their breathing, but in an easy approach. If you are too focused on your breath intake and exhalation, you can end up having a stitch.
Keep in mind, that your whole body gets conditioned through running, also your lungs.
So by starting with easy runs, in a pace that allows you to chat without choking, you will breathe naturally. Most athletes breathe solely through their nose, but they can intake 4 times more air than a beginner. Therefore, you do not have to stick to every rule you come across, as your breathing will adjust with your fitness level.
Learn to breathe deeply
When starting running, make sure your posture is straight, your arms rest easy on your sides with your elbows slightly angled. Let your body naturally adapt, let your arms swing with the motion and progress slowly into a comfortable running pace. Deep breaths are always helpful. Your body tells you what you need, when you are gasping for air, try to take calm deep inhales into your tummy. Exhale gently. This floats your body with fresh oxygen, and breathing calmly lowers your heart rate.
How to breath, while running fast? If you enjoy running fast, you will automatically breathe through your mouth, as your heart rate goes up along with your breathing. Please take breaks when you feel like it. Running at a beginner’s level usually starts by checking your endurance. Going at a steady pace, and even taking breaks to walk a while, will only help your body to adjust.
You will progress gradually, if you do not force it. Once your movement and breathing is in balance, you can get competitive with yourself and challenge your times and distances.