When you first start running, you will likely find yourself alternating running and walking. You will also hear the term “interval training” in referring to the walk/run method. This is a widely accepted method that you can use as long as you like. I saw many people use this method during my marathons. Most ultra runners use this technique to help them finish races from 31 miles to 200 miles. I have seen people walk/run many different kinds of distances at races. It is not failure to walk. If you meet your goal by alternating walking and running, you are a finisher. You can start out with walking to warm up and then running as long as your body will allow (for many people this can be 30 seconds or less). Then you walk to 1 to 3 minutes for recovery and run again. You want to work your way up slowly. If you run too much in the beginning, you increase your risk of injury. I would suggest total training times of 15 to 30 minutes when you first start out. The bulk of that should be done walking. Many people use this method successfully to prepare for a 5K. Just be sure to give yourself 10 to 12 weeks to build up your time on your feet. Your goal is to not get injured and discouraged during your training.
When you are running, you will find a cadence, the speed at which your feet move, that works for you and is comfortable. I would suggest that you use an app on your phone to help you find your natural cadence. Then, you can experiment to see how you can change your cadence to increase your speed. If you watch sprinters run, they use really long, quick strides. For the average runner, you can increase your speed by taking smaller, faster steps when you run. More steps per minute translates into a faster pace. I am a short person, so I already have a short stride. I found that if I quickened my landings and shortened my strides I could run faster, and it was easier on my body. When I use a longer stride, I land harder, and it hurts my joints more. Try smaller, faster strides and see how it changes your pace.