Yugioh TCG: How do Trap Cards work?

Trap cards

Cards that are activated in response to certain situations, most often when an opponent activates an effect or attacks. They are set face down on the field and cannot be activated on the turn they were placed down under normal conditions (some card effects may allow this). Some are used to destroy an attacking monster, negate battle damage, or possibly redirect damage back to the opponent, though, these effects may differ. There are three types of trap cards:

1. Normal (通常 Tsūjō^?, no icon)

A standard trap card. Certain normal traps may be treated as Equip cards but are still considered normal trap cards.

2. Continuous (永続 Eizoku^?, infinity symbol)

Upon activation, the card's effect remains in play until its destruction circumstances are fulfilled.

3. Counter (カウンター Kauntā^?, curved arrow)

Trap cards that can be activated in response to the activation of other trap cards. Once a Counter trap is activated, no cards except for other Counter traps may be activated in response to it.