DW, like its parent AW, takes for granted that RPGing is a
conversation. The participants say things, and in the process of, and as a result of, saying those things, they create a shared fiction. That shared fiction concerns the fantasy adventures of some D&D-style protagonists.
DW, like its parent AW, sets out a procedure for that conversation to follow: it's not free-form. As
@hawkeyefan posted not a long way upthread, it specifies certain "triggers" for whose job it is to say what.
The most common thing for a player (cf GM) to say is
what it is that their character does. When they say that, either
it will trigger a player-side move, or it will not. The list of player-side moves is finite, and each states a trigger, which (with one or two exceptions that can be ignored for present purposes) takes the form of a description of an action in the fiction, like
when you take aim and shoot at an enemy in range (in DW, this triggers the player-side move Volley). If a player-side move is triggered, the dice must be rolled (because of the rule "if you do it, you do it") and depending on the result (after modifiers), either the player or the GM (sometimes both) are instructed to add something further to the conversation (eg one possible result for Volley is that "You have to move to get the shot placing you in danger as described by the GM" - so the player describes "I move to get in my shot" and the GM describes the resulting danger, drawing on the established elements of the shared fiction (as per the earlier conversation), plus whatever other ideas they might have, to do so).
If the result of the roll for a player-side move is 6 or less, then the GM gets to make as hard a move as they like. More on this shortly.
If a player describes their PC doing something that does
not trigger a player-side move, then the rule is that the GM "makes a move", that is, says something in the contribution. This should be a soft move,
unless the player is handing the GM a golden opportunity to follow through on a threat that has already been established in the shared fiction (as a result of an earlier move).
Sometimes, in play, the players don't describe their PCs doing things, but rather look to the GM to get a sense of what is going on around them, or to get some framing, or just because they're not sure what happens next. When this happens, the GM "makes a move". Just as mentioned in the previous paragraph, this should be a soft move
unless the players are handing the GM a golden opportunity to follow through on an earlier move.
When the GM makes a soft move, this means describing something in the fiction that increases the risk, or threat, or apprehension, or stakes - to speak in general terms, it contributes to the rising action. But a soft move does
not foreclose the current aspiration the player has for their PC in the fictional situation. By way of contrast, a hard move consists in the GM describing something that
does, in some fashion or to some extent, foreclose in that way. In other words, a hard move is immediate and irrevocable in its effect. The most generic example of a hard move is dealing damage, but obviously in many situations other, perhaps more interesting, hard moves will be possible.
The basic sequence of play that results from these rules is this: there is rising action, as the players describe their PCs doing things that do not trigger player-side moves, and the GM responds with soft moves. Then a player has their PC do something that triggers a player-side move; or, perhaps a player has their PC do something that hands the GM an opportunity. In the latter case, the rising action resolves into some sort of crisis or climax (as the GM makes a hard move). In the former case, depending on the result of the dice roll, the same may be true; or, perhaps, the result of the dice roll is another soft move (eg as per the example of Volley above, the GM describes the PC moving into a new sort of danger); or, perhaps the result of the dice roll is some sort of victory for the PC (eg in dealing their damage as a result of Volley, they kill their enemy, just ending the threat they are facing).
The most radical contrasts with D&D, as typically played are these: (i) the GM can only make a hard move in the situations I've described; the GM has no licence to make a hard move because that's what would follow from the logic of their as-yet-unrevealed prep; (ii) the GM is not permitted to narrate fiction which is not either a hard move (some sort of immediate, irrevocable crisis or climax) or a soft move (some sort of contribution to the rising action). In other words, "nothing happens" is not a legitimate move for a DW or AW GM.
<snip>
DW emphasises the GM's role in either contributing to the rising action (soft moves) or - in the circumstances that the rules dictate - contributing to crisis or climax (hard moves). When making those contributions, the GM will naturally draw on ideas about jails, and legal systems, and NPCs, but
in aid of performing their job in the conversation as dictated by the rules of the game.