Counters will cancel out and be removed, but actual cards will not (they effectively cancel out, but they do not get removed unless other cards act specifically to remove them).
This is a state-based effect, which means it happens faster than you can tournament legally react to it (you can react to cards or effects that try to add one of the counters, but once the counter effects the card you cannot do anything to stop the cancellation).
People use this rule to keep creatures with "Persist" in play longer than they normally are.
No, a creature is not considered a spell in Magic: The Gathering.
No, a planeswalker is not considered a creature in Magic: The Gathering.
No, in Magic: The Gathering, you can only block one creature with one creature.
When a Magic: The Gathering creature dies, it is put into the graveyard from the battlefield.
Yes, in a game of Magic: The Gathering, you have to tap a creature to use it to block an attacking creature.
You can regenerate a creature in Magic: The Gathering when it would be destroyed, by paying the regeneration cost specified on the card.
No, a creature in Magic: The Gathering cannot be regenerated if it has the ability "can't be regenerated."
Yes, "Changeling" is a creature type in Magic: The Gathering. Changeling creatures have the ability to take on the characteristics of any creature type.
Yes, in Magic: The Gathering, you can block more than one creature with a single creature if it has the ability to do so.
In a game of Magic: The Gathering, multiple creatures can block a single creature.
No, in Magic: The Gathering, each creature can only block one attacker at a time.
When a creature with trample attacks a creature with protection in Magic: The Gathering, the attacking creature can assign excess damage to the defending player or planeswalker, bypassing the protected creature.