From your studies on ink manipulation through arcane infusion, you've learned how to project a beam of energized ink at a target within range. Make a ranged spell attack against the target. On a hit, the target takes 1d8 acid damage and is marked until the end of your next turn. This mark helps you or your allies to aim and hit the target, giving +1 bonus to the next attack roll against the target.
The spell creates more than one beam when you reach higher levels - two beams at 5th level, three beams at 11th level, and four beams at 17th level. you can direct the beams at the same target or at different ones (each target can be simultaneously marked). Make a separate attack roll for each beam.