A rising line, and one button
Crash strips a casino game down to almost nothing. A number starts at 1.00x and begins climbing. It might stop at 1.03x. It might climb past 50x. You have no way of knowing which, and the only thing you can do is press a button labelled Cash Out. Press it while the number is still rising and you keep whatever it said at that moment. Fail to press it before the line breaks and your bet is gone.
That is the complete rule set of the crash casino game. There is nothing to learn beyond it, no hands, no boards, no symbols. It is the purest expression of a single question: how greedy are you willing to be, and for how long?
It is also, for a beginner, the most emotionally intense game on this site, and that is worth knowing before you start. The tension is not incidental to crash. It is the product.
The rest of this guide assumes you have never played a casino game and do not know the vocabulary. That is genuinely the best way to arrive at a crash game casino format, because there is very little to unlearn, and because the few things worth knowing are the things experienced players are most likely to have talked themselves out of believing.