Okay, variables.
You can set a variable in these games to be equal to a huge variety of things-- the X or Y position of a character or event, a random number, a specific number, the terrain tag of the terrain the character is standing on, almost anything. (You do this with the "Control Variables" command in XP.)
You can then manipulate those variables (Adding one to a chapter count periodically, for example, or subtracting an enemy's position from a player's to find the range between the two of them.)
You can also make conditional branches, or set the page conditions for an event using them.
For example, let's say that in my game, I want the town guard, who's an incredible gossip, to comment on what's going on in the game at all times when you talk to him. I'll give his event a lot of pages, and have the condition for each page be the "Chapter" variable. Now, whenever a major event happens in the game, I'll increase the "Chapter" variable by one, and he'll say something about the recent events when you talk to him.
Is that at all clear?