I just started playing this game and it is not clear to me exactly what committed cards and non-committed cards can and cannot do. Are only committed cards allowed to defend and attack? Can you use the abilities of cards that aren't committed?

I was under the impression that you can only attack and defend with cards that are committed, but after reading around a bit it sounds like all character cards in play are able to attack, defend, use abilities, etc.

Let's use the word "commit" to refer only to cards who are "committed" to the quest during the questing phase.

For cards that are turned sideways, use the more general term "exhausted." You will also see players refer to this as "tapping" or "tapped" since that is the terminology used in some other popular games (notably, Magic).

You must exhaust a card in order to: declare it as an attacker, declare it as a defender, or commit it to a quest. You can use a card's Action text if you can pay the cost. Sometimes the cost says that you need to exhaust the character (example: if you have "Steward of Gondor," you must be able to exhaust it in order to use its Action... so you can only use it once per round. The hero Beravor works the same way-- you have to be able to exhaust her. If she is already exhausted, you cannot use her Action).

If the Action or Response on a card does not explicitly say that you need to exhaust a card to do it, you can use it without exhausting a card. For example, the new hero Grima doesn't say anything about exhausting a card. You can trigger his Action even if he is exhausted.

Hope this helps.

edit: also, taking damage from an undefended attack... this is done regardless of whether or not a card is exhausted. Whether a card is exhausted or readied, it may take damage from an undefended attack.

Let's use the word "commit" to refer only to cards who are "committed" to the quest during the questing phase.

For cards that are turned sideways, use the more general term "exhausted." You will also see players refer to this as "tapping" or "tapped" since that is the terminology used in some other popular games (notably, Magic).

You must exhaust a card in order to: declare it as an attacker, declare it as a defender, or commit it to a quest. You can use a card's Action text if you can pay the cost. Sometimes the cost says that you need to exhaust the character (example: if you have "Steward of Gondor," you must be able to exhaust it in order to use its Action... so you can only use it once per round. The hero Beravor works the same way-- you have to be able to exhaust her. If she is already exhausted, you cannot use her Action).

If the Action or Response on a card does not explicitly say that you need to exhaust a card to do it, you can use it without exhausting a card. For example, the new hero Grima doesn't say anything about exhausting a card. You can trigger his Action even if he is exhausted.

Hope this helps.

edit: also, taking damage from an undefended attack... this is done regardless of whether or not a card is exhausted. Whether a card is exhausted or readied, it may take damage from an undefended attack.

To add on to the later part of undefended attacks. "If an attack is undefended, all the damage from the attack must be assigned to a single hero controlled by the active player. Allies can not take damage from undefended attacks [unless otherwise specified in the card text, such as Gollum in Return to Mirkwood]. If a defending character leaves play or is removed from combat before damage is assigned, the attack is considered undefended."

Reference from the Rules of Play