Do a slow buildup for the periods of time you run. Walk inbetween them, for example like this: 2 mins running, 3 mins walking, 2 mins running, 3 mins walking, 2 mins running, 3 mins walking, 2 mins running, 3 mins walking.
If you can do that without getting real tired, you can build it up to 3 mins running ech time, then 5, then 7, etc.
Shoes are superimportant, best go and buy them at a store where the salespeople know more about them than just the way they look.