Jokers are worth 50 points each. Aces and 2's are worth 20 points each. The next lowest scoring is with 8 - K's being worth 10 points each. The lowest scoring cards are 4, 5, 6, 7 and black 3's which are worth 5 points each.
Red 3's are 100 points if your team has at least one meld when the round has ended. You would be penalized 100 points if you do not have a meld when the round has ended. Should you get all 4 red 3's; the score is doubled to 800 points and the scoring is consistent with the afore-mentioned rules. When and if you get a red three dealt to you, it goes into a special pile and you receive another card. This has nothing to do with picking up cards on your turn; it is a totally separate play.
Natural Canastas get 500 points each. A natural Canasta is made with all seven cards being the same rank. There are no wild cards at all included in a natural Canasta. If you make a mixed Canasta, the bonus points are limited to 300. The mixed Canastas include up to three wild cards. Any extra cards added to a Canasta over the needed seven are ignored as far as points.
The points count for you or against you at the end of each round. When one team goes out, if these cards are in your melds, those points count for you. Whether or not your team goes out, the above cards left in your hand count against you.
The team that goes out first in a round gets 100 additional points.
Using a black three to make pickups from the face up pile impossible is a good strategy, even if the face up pile is frozen by a Joker or a two. Remember, when a pile is frozen, the next player can pick up if they have at least two cards of the same rank that you laid down. You are usually not wasting a black three if you think there is a chance that the next player could pick up the card you laid down.
Frozen piles are wonderful if you want to possibly prohibit the next player from picking up a pile. This is especially true if they have many melds of different cards; and you have almost nothing to lay down except what is already on the board in their melds.