Of course, since this is the Beginner Box forum, you probably don't have the Core Rulebook, and page references would make little sense to you. I can't give you BB page references, because I don't have it myself, but I can surely explain how traps work.
Basically, any trap has a Trigger, a Reset, and an Effect. The trigger is what makes it go off; it could be "touch", which means it goes off when someone steps on the pressure plate or kicks the trip-wire; or "proximity" which means it goes off whenever someone gets close (this usually requires an alarm spell; or some other things. Specifics will be explained in the accompanying text for a given trap. For example the room description might say, "The trap hits the first person who steps on the square in front of the door to room 4." This would be an example of a touch trap.
The reset describes how it sets itself up to go off again, once the first foolish adventurer has stepped in it. For most traps, this is "none," which means it's one-shot and that's it; or "manual," i.e. someone has to come by and wind it back up (like a mousetrap, only bigger). Particularly advanced mechanical or magical traps might reset themselves automatically after some amount of time (usually a few rounds).
The effect is what happens when some fool adventurer steps in it. Often it's just an attack, like "Atk +15 ranged (1d8+1/×3)". All this means is that whoever triggered it gets hit by that attack; in this case the trap attacks just like a creature would, with a +15 bonus, and it deals 1d8+1 damage if it hits, with triple damage if it critically hits. Sometimes it's a spell effect, and it will describe what spell it is and how much damage it does, and often the reflex DC for avoiding it. For example, a burning hands trap might say "spell effect burning hands (2d4 fire damage, DC 11 Reflex save for half damage); multiple targets (all targets in a 15-ft.-long cone)" which pretty much does what it says on the tin: it casts burning hands as though a 2nd-level wizard were standing on the trap blasting the heroes.
At the top of the trap listing (right under the name and CR) it will have numbers for Perception and Disable Device. These are the difficulties to spot the trap before it goes off, and to disable it without setting it off in the process. Most mundane traps will have 20 for both of these numbers, so your rogue can roll a d20, add her Perception + Trapfinding bonus, and if she gets 20 or more, she spotted the trap. She then rolls a d20 + her Disable Device bonus to disassemble it before the fighter steps in it; if she misses by more than 5 she blew it up in her own face instead. Magical traps are usually a lot tougher to notice and disable, and only rogues can even attempt it.
Good luck playing! Be sure to tell us about it afterward, Beginner Box stories are always fun to read.
