The walkway is clearly marked, but you need to understand the components of the walk:
You will depart MGM heading toward the parking lot. Follow the sidewalk along the left hand side until you hit the path. The path runs alongside the canal between the BoardWalk Villas and the Swan. You wiill be on the BWV side of the canal. Follow it to the end, emerging on the BW between JellyRolls and the Atlantic Dance Club. Turn right onto the BW and follow it past the ESPN Club, and continue to the bridge leading to the Epcot International Gateway entrance. This takes you into Epcot between England and France in the World Showcase.
I can do this in 20 minutes at a reasonable pace, unless I stop along the BW for some refreshments (Big River brewpub, Spoodles pizza window, and ESPN Club are good options).
Ralph