I walked many miles at a convention the past 3 days & my calves are very tight & my left shin is very painful to the touch, almost like it is bruised. i'm not a runner & was not exercising before this?

Overuse: Your symptoms are likely related to overuse. Rest, heating pad, antiinflammatiry medication like Ibuprofen or naprosyn, (naproxen) and aggressive hydration should help alleviate the discomfort.

Pulled muscle: You're most likely describing a pulled muscle or muscle strain, especially if you're not used to that amount of walking. Rice is a reasonable approach to most injuries eg rest, ice, compression & elevation. Stretching helps. Common otc acetaminophen, Ibuprofen & Naproxen are fine (just don't take latter 2 together). Go see your family doc if pain progresses or persists. Start exercise once painfre.