Assume the average fuel canister is the size of a 6 meter in diameter cylinder about 5 meters long. A floating laser 'tug' fires a laser at this plug of reaction mass. One quick pulse to vaporize a layer off the bottom. Then a heavy pulse to turn the vapor to super heated plasma. Keep repeating these cycle up a couple hundred times a second, and you have a laser rocket.
Specific impulse is limited by the type of reaction mass and the heat the laser brings it to.
Course corrections are handled in two ways. The first involves aiming the beam to one side of the base, rather than in the center. The uneven thrust will turn the canister, and subsequent pulses will thrust along the new vector. Precise course changes are handled by burning a bit of reaction mass off the side of a canister as it passes a laser tug. This would give precisely controlled lateral thrust.