The second ability is cumulative. That is, each creature you control with any +1/+1 counters on it can block an additional creature for each Cenn’s Tactician you control. Cenn’s Tactician doesn’t care whether the creature has any +1/+1 counters on it beyond the first.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.