Newbie-ish question: "1 on a d6"?

[Rothbard]

Alright, tried GMing a little module with my wife last night just to start to get the feel of GMing. Ran across this in the "kidnapped" module:

"The mortar holding the bricks from the north wall is starting to crumble. Any character looking for secret doors (1 on a d6, 1-2 on a d6 if the character have darkvision or found a way to light the room) will discover this."

Does this mean that they MUST roll those values on a d6, and if they do not they fail the roll, or does it mean that they at LEAST get 1 (which it seems would make the dice roll useless.)?

This is a really clueless question, I know. Please forgive my ignorance, as I'm used to ability rolls using d20s (where the philosophy is, you must roll high enough to pass the check).

[Dimirag]

Those kind of rolls means that a d6 is rolled and if the given number appears then something happens, 1 in a d6 means that on a roll of 1 the character discovers something and on a roll of 2-6 they don't.
These rolls works better if the GM is the one rolling as it keeps suspense and possible data out of the player's hands

[Rothbard]

Thanks. I knew the answer would be fairly obvious. I'm going to try to keep as much of those checks on my side of the GM screen.

[mTeasdale]

And how did it goes ? I'm pretty curious, I haven't heard much feedback and comments on this, except from my playtest run.