Everyone else has covered the side stitch issue pretty well – slow down, breathe (at an easy training pace, you should be able to hold a fairly simple conversation as you run. If you can’t get out five words without panting, you’re going too fast), and if it hurts too much to keep running, slow to a walk but keep moving. Raise your arms up over your head to help stretch out your torso & diaphagm.
As for the shin pains, beginning runners often aggravate the fairly weak muscles in the front of the shin due to bad biomechanics. With easy, regular exercise, you can build up those muscles and the pain will go away, but in the interim, here are some things to think about:
Shoes – if you’re seriously going to take up running as exercise, find a local running store and buy a pair of real running shoes there. Most places will have you run on a treadmill for a bit as they film your feet and ankles, and will be able to show you a shoe that is appropriate for your particular running gait. Just picking out a pair of shoes that “feel good” or look pretty or are cheap can make things worse. A good pair of running shoes may cost $80-$120, but if you’re doing anything more than walking, getting shoes that properly distribute weight and impact is essential to avoiding injury.
Footfall – one thing that will really make your shins hurt is if you’re not properly landing (e.g. you’ll get serious shin pain quickly if you’re flexing your foot upwards too much in order to land on your heel). Different people have different styles, but by and large, don’t make the common mistake of trying to land squarely on your heel – doing so causes you to overflex at the ankle and will make shin pain much worse. Try to make the first part of your foot to touch the ground be the midpoint between your arch and your heel. A good way to fix footfall problems is to pretend that you’re running on broken glass, trying to land each step as softly and quietly as possible. This will help stop you from “stomping” on the ground as many new runners do. You’ll also want to avoid the hardest surfaces whenever possible, at least until your ankle and knee muscles build up a bit – concrete and cement (i.e. sidewalks) are the worst; asphalt is a little better; hard-packed dirt and gravel/cinder trails are pretty good; your local high school track might have a cushioned rubber surface that is close to ideal.
Gait – New runners usually haven’t figured out the right gait for easy body movement and tense up muscles that should be relaxed. Most runners don’t lean forward enough and try to get their propulsion mostly from pushing off with their toes. This will exacerbate any shin pain. How far you lean will depend somewhat on how fast you’re running, but ideally, much of your propulsion should come from the fact that your center of gravity is ahead of, rather than over, your feet. Have a friend put their hand on your chest and then lean into them until you are at a point when you’d stumble or fall if they took their hand away – that’s the body angle you want when running.
The only other casual biomechanical advice I can give is to try different things as you run, and see what feels best. I can’t discourage you enough from wearing an MP3 player to distract you when you run. Instead, spend the time trying to be conscious of what you’re doing with each part of your body and experiment with each one to see how it affects you – e.g. run a few hundred yards with your butt a little lower to work your quads more; try holding your arms higher or lower or swing them more or less; try holding your shoulders more forward or back; your chin higher or lower, etc. Becoming conscious of your body will not only lead you to your most natural and efficient running form, but it will get you more attuned to how you’re feeling along the way and teach you to differentiate between the “this hurts because I’m pushing myself” pain and the “this hurts because I’m injuring myself” pain.
Start slow, increase distance gently, breathe easily and deeply, and if nothing else, keep moving forward. Good luck.