Walkers are vehicles that have legs instead of tracks or wheels, the most common being huge war machines called Dreadnoughts. Walkers move like infantry so they can move up to 6" in the movement phase and then charge up to 6" in the assault phase if the enemy are within 6". Difficult terrain affects walkers just as it does infantry. Walkers moving into, out of or through difficult terrain have to roll 2D6 and use the highest result as the maximum distance they may move that turn.
Walkers have sophisticated weapon systems that are fully integrated with their crew so they can engage targets on the move more easily than other vehicles. This means they can always fire two weapons (one from each side/arm) regardless of whether they've moved or not. Walkers who do not move can fire all their weapons.