Zone defense is defending space in predefined formation instead of defending individuals. If you look from the perspective of the basketball, you'll see the defense aligned in two or three lines. Raptors played 1-2-2 last night with Siakam at the top. That means when the ball is in the middle of the floor you'll see Siakam at front, Lowry and FVV were closely behind him and Ibaka and Kawhi were near the basket.
Zone moves with the ball so wherever the ball is on the floor you'll see the same formation between it and the basket. Zone takes away dribble penetration, post ups and offensive sets. It requires offense to adjust and attack in a specific way, fundamentally different from usual scheme.
That usually includes flashing a big to high post and getting him the ball. You want to overload one side of the floor by moving extra players there. Because zone is set formation, just by placing three guys on one side of the floor you are forcing the defense to guard them with two guys or break formation once the ball gets there. And it can get there cleanly once a tall guy has it at high post. That player is usually a threat in that spot either for drive or a jump shot so it forces the zone to compress towards him. Moving the ball out of there to the overloaded side, setting a screen (you have extra personnel to do it) can get you an easy open shot. But you really want to force the defense to compress and stretch while you purposefully move the ball and bodies around and find a high percentage shot.
Strategies vary and depend both on personnel and type of zone played.
Attacking a zone requires some practice and smart players that are able to switch focus on the fly and remain disciplined. Once figured out it starts bleeding points quickly. Due to it's nature of covering space rather than personnel it can also often allow offensive rebounds at high rate. Good and great teams are prepared for it and usually dismantle it quickly and force the defense to go back to man-to-man in a few possessions. But young or bad teams have major issues with it.
Zone used to be illegal in NBA. They allowed it once they got rid of the hand check on the perimeter but with a twist, they added 'defensive three seconds in the key' which really impacts how you play zone(and team defense in general). You can't just park your center near the rim and having him stand there and wait for blocks. This rule is brilliant in general, zone or not. Imagine if Gobert and Whiteside were allowed to just stand in the key on defense ready to shut down any drive to the basket. There isn't such a rule outside of NBA and it really sucks. That and smaller court makes European basketball barely watchable for me because it just rewards defense and unnaturally closes the gap between good and not so good players.
Raptors started using zone few years back but not for extended stretches like this season. Short stints and often when defending out of time out plays. That is great use for zone because ATOs are prepared and practiced for so you've got the offense coming in hyped for something they know works and looking for an easy basket...and boom..there's just a wall of humans there not giving a fuck about your cute set. That forces adjustments and at that point defense is halfway to getting a stop. And nothing is stopping you to go back to man to man midway through possession and force yet another adjustment. Of course, it requires smart and flexible defensive personnel.
More and more teams are using zone this season for not so short stretches and looking for ways to gain an advantage and change the rhythm of the game. It has great use in that regard. But the more it is used, the more teams will prepare for it and less effective it will be because once attacked properly, it falls apart like a house of cards. Nurse has done a good job of dozing it from time to time. Recent game in Miami is a good example of throwing off the Heat in the second half. Practically won the game with it after being down 16. And Miami got that lead by playing a lot of zone in the first half. It is good regular season tactic because there isn't enough practice time to prepare it and you can get a team out of their comfort zone even if they are prepared because of fatigue, rhythm, sort of shooting day you are having etc.. We lost a game to Boston last year because they played zone in the second half and we couldn't capitalize on it even though we were getting good shots and attacking it properly. Made a few unforced turnovers, missed a few bunnies and wide open shots and boom. Just weren't sharp enough that day to execute it properly.
I don't think it can do much in end game scenarios, where it would be too risky, or in playoffs, where there's more than enough time to prepare. But it is good trick to have in regular season, especially against young, rebuilding teams like Hawks who were quite lost against it and their offense looked like a headless chicken running around.