Speed work is huge for new runners. Most new runners start with easy efforts which is great for your aerobic engine, but as you start to run more miles its important to also do speed work. This can be interval or fartlek runs. This will help with your body's ability to utilize oxygen efficiently. When you're running faster, your body will adapt to getting more comfortable at that pace. It's not gonna happen right away, but the more speed work you do, the better that you will get.