There is a much simpler way to get to that same
Walmart. It's a teensy bit longer but it avoids the traffic around International and World Drive, which IMO is kind of an easy place to get turned around and confused.
To use the more straightforward route, take the south exit out of the Airport and get on 417 headed for WDW, as the PP said. (Also, note that 417 is the Greenway, not the Beeline/Beachline). However, do NOT get off at International Drive. Keep going a little further, and ...
Get off on Osceola Parkway, then turn LEFT at the bottom of the ramp (not right as you would to go to WDW, you are now going away from WDW on Osceola). Continue to the Poinciana Exit on Osceola (a bit less than a mile), then at that bottom of that ramp turn left on Poinciana and drive under Osceola. The Walmart is right there on the corner on your left.
To go to WDW from there, go back the way you came into the Walmart (on Poinciana), then get back on Osceola headed back toward WDW, then just follow the signs onto the property.