They grant freedom to re-spin and move 1 point to the left to the adjacent reel. As long as there is at least one walking Wild on the reel, you can get the Walking Wild feature. Walking Wilds occurs more often during free spins.
It will appear after winning and will give you a victory multiplier. In the base game, you will randomly apply the winning rotation between the x2 and x5 multipliers, and in the free spin, you will get the same multiplier applied to all winning rotations. In Belgrade, the small train will travel from the right side of the reel to the left.