Just walk straight out the BLT main entrance and you will see signs as you near the road pointing out the sidewalk to MK. (It's all fairly obvious, just start walking toward MK). One night I walked back from MK to BLT and as tired and sore as I was from walking all day, I still made it in 7 minutes.
I don't think that the monorail is faster. From the Contemporary to MK you would need to stay on the resort loop and stop at TTC, Poly and GF before arriving at MK or transfer at TTC to the MK express loop. So if you have the energy or children aren't a factor, then walking to MK is an easy thing to do.