While it's true that running alone won't do for significant weightloss, I always had the feeling that it helps a lot. It seems that I can get much more workout from 1 hour of running than 1 hour of cycling. Also I like it as alternative to indoor cycling in winter.

The best tip for me would have been: start really really slow. Try to focus on your form (I see awful things on my running trail in regards of posture and footwork everyday, those people don't do themselves any good).
It's also very personal. My husband had no problems to run a 5k when we started out. I could barely run the distance between 2 street lamps before my shins where aching I'm not a natural when it comes to running I guess.
So I walked a lot in the beginning. It took me a year to run 5k without having to walk. It can help to monitor your pulse and try to keep between a reasonable margin by alternating between walking and running.
That stitch in your side: breathe and relax. Go slower.