I wouldn't call myself an expert. Like you Dan, I walked for a while and then I felt like I was speed walking, and eventually I wanted to run. I just ran until I my heart rate was about 155 and then stopped and walked for a bit until it was under 120 and then ran again, rinse and repeat. I did this for an hour or so, doing about at 5K.

This will vary for everyone. You're younger, so heart rate will probably should go higher. Each day I ran or each week I would push myself to run longer or farther. Eventually I got up to a 5K, running the entire time. Before I hit that milestone though, I needed new shoes. I got myself a nice pair of Skechers running shoes. I also bought myself a pair of Shokz bone conducting headphones. My earbuds were lose or falling out. I fucking love them. I also started wearing boxer briefs when I run. Never wore them before. I've been wearing boxes since I was 11. The boxer briefs keep the junk from bouncing all around. And lastly I eventually bought an arm band to strap my phone to my arm. I always listen to music or podcasts. Shrug.