Crash gambling works on a multiplier that climbs from one and stops at a random point. To play, a player places a bet before the round, then chooses when to cash out; leaving before the crash pays the stake times the multiplier reached, staying too long loses it. The crash point comes from an algorithm that many sites publish as provably fair, so any round can be checked afterwards. No betting strategy changes where the next crash lands.
Crash is not profitable over time, whatever system a player follows. Every multiplier carries the same built in edge, usually one to five percent, so cashing out early wins often but small, and waiting for large multipliers wins rarely. Anyone asking how to win at crash is really asking how to lose slowly: a fixed cash out point and a fixed budget keep a session short, but they cannot put the house edge in the player's hands.
Plinko odds depend on how many rows the board has and which risk level a player picks; more rows and higher risk widen the gap between the rare edge slots and the common middle ones. Whether plinko is rigged or legit comes down to the site: a licensed game with provably fair results can be checked, an unlicensed one cannot. Plinko for real money makes money for the casino through its edge, and a free demo lets anyone play plinko without money, subject to the legal age in their country.